Accuracy of Partial Weight Bearing After Autologous Chondrocyte Implantation

Article Outline

• Abstract
• Methods
• Results
• Discussion
  • Study Limitations
• Conclusions
• References
• Copyright

Abstract 

Ebert JR, Ackland TR, Lloyd DG, Wood DJ. Accuracy of partial weight bearing after autologous chondrocyte implantation.

Objective

To determine whether patients can accurately replicate and retain weight-bearing restrictions in both stationary (static) and dynamic conditions after autologous chondrocyte implantation (ACI).

Design

Case series.

Setting

Rehabilitation clinic.

Participants

A consecutive sample of patients (N=48) who had undergone ACI to a medial or lateral femoral condylar defect in the knee.

Interventions

Patients were trained to partially weight bear using bathroom scales and forearm crutches prior to assessment.

Main Outcome Measures

A force platform was used to measure peak vertical ground reaction forces in patients during static and dynamic conditions immediately after weight-bearing instruction and training, and again during gait 7 days after training.

Results

Immediately after instruction and weight-bearing practice on a set of scales, patients exerted a mean of 15.8% body weight more than expected during walking for 20% weight-bearing trials, 8.3% more for the 40% trials, 11.9% more for the 60% trials, and 1.2% less for the prescribed 80% trials. Accuracy of weight-bearing replication improved across all weight-bearing levels when assessed 7 days later, when patients exerted a mean of 6.6% body weight more than expected during walking for 20% weight-bearing trials (9.2% body weight improvement), 4.2% more for the 40% trials (4.1% body weight improvement), 9.9% more for the 60% trials (2% body weight improvement), and 0.2% more for the 60% trials (1% body weight improvement).

Conclusions

Patients were unable to follow weight-bearing restrictions after instruction and practice on a set of scales, and patients were unable to replicate weight-bearing levels in both static and dynamic conditions.

Key Words: Rehabilitation, Weight-bearing

List of Abbreviations: ACI, autologous chondrocyte implantation, BW, body weight, PWB, partial weight bearing

AS A REPAIR PROCEDURE, ACI has shown early clinical success in the treatment of focal articular cartilage defects in the knee.¹, ², ³, ⁴ The general ACI procedure involves isolating and culturing a patient's own chondrocytes in vitro and reimplantation of those cells into the cartilage defect; therefore, over time, development and remodeling of the repair tissue into hyaline-like cartilage can occur. Postoperative rehabilitation after ACI involves a gradual and progressive program that emphasizes full motion, controlled exercises, and progressive load bearing.² PWB throughout the early stages after ACI is encouraged⁵ to provide protection and progressive stimulation of cells, without overloading the graft; however, it is unknown whether patients can replicate these desired loads, potentially hindering optimal short- and long-term development of the repair tissue.

Robertson et al⁶ proposed that rehabilitation should consist of a structured load-bearing program progressing from 20% to 100% BW over a 3- to 4-month postoperative period. Numerous methods exist for teaching this progressive PWB program to patients, including verbal instruction,⁷ pressure applied to the hand of a licensed physical therapist,⁸ the use of standard bathroom scales,⁵, ⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁴ “limb load monitors”¹⁵ or pressure insoles,¹⁶, ¹⁷ and force monitoring platforms.⁸ The bathroom scale method is recognized as one of the most common and practical methods of teaching PWB.⁵ However, mixed results surround the evaluation of this method as an effective tool for teaching PWB, whereby both good¹⁰, ¹² and poor⁸, ⁹, ¹³, ¹⁴, ¹⁷ PWB replication ability has been reported.

A number of issues arise pertaining to the use of PWB for ACI rehabilitation. First, unidirectional loading in a stationary position fails to reproduce the situation experienced during dynamic gait⁸ whereby body and limb accelerations are introduced. Second, the patient must be able not only to replicate the prescribed PWB levels accurately after instruction, but also to retain that information over an extended period. Third, much of the existing research has explored PWB ability at only 1 specified weight-bearing level,⁸, ⁹, ¹⁰, ¹¹, ¹², ¹⁷, ¹⁸, ¹⁹ and in unaffected subjects.⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁷, ¹⁸ Factors in patients such as pain⁹ and reduced muscle power²⁰ affect PWB ability, as may an altered mental state and fragility after the operative procedure.

Presuming a direct relationship between ground reaction force experienced at the feet and loading experienced at the articular surface, the purpose of graduated PWB in ACI rehabilitation is to provide both protection and an ongoing stimulus to developing repair tissue. Postoperative rehabilitation for the ACI procedure focuses on increasing load bearing in gait over time, which provides the optimal stimulus for developing chondrocytes at each postoperative stage, without overload, and possible delamination of the graft. The accuracy of load-bearing replication and retention during PWB gait throughout the duration of the rehabilitation program is based on the ability of each patient to learn, replicate, retain, and exhibit the desired loads while walking. However, it is unknown whether patients can actually carry out this theoretical program.

Our first 2 hypotheses were that patients undergoing ACI could not replicate vertical ground reaction force loading within 5% of patient BW in both static and dynamic conditions immediately after instruction, across a range of PWB loads throughout the rehabilitation period. Third, we hypothesized that patients could not replicate these loads within 5% of patient BW dynamically after a 7-day instruction-retest interval, and fourth, that there would be no significant improvement over the 7-day period across all PWB loads. Finally, we hypothesized that patients undergoing ACI who were poor at replicating vertical loads in a static condition would also be poor at replicating those loads during walking.

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Methods 

We instructed 48 patients (31 men, 17 women) who had undergone ACI to the knee how to achieve PWB loading at 20%, 40%, 60%, and 80% of their individual BW using the bathroom scale method. After instruction and practice of each of the nominated weight-bearing levels, the ability to replicate the nominated loads within 5% of BW in both a stationary (static position: a situation that duplicated the practice setting) and during walking using a force platform was assessed. This assessment took place both immediately (static and dynamic) and 7 days after instruction (dynamic).

Patients who had undergone ACI to localized, full-thickness medial or lateral femoral condylar defects (<10cm² on magnetic resonance imaging) to the knee participated in this study. Patients with multiple articular cartilage defects were included, as were those with ligamentous deficiencies provided they were addressed before or at the time of ACI grafting. Patients with isolated trochlea or patella defects were excluded, as were those presenting with ongoing progressive inflammatory arthritis or varus-valgus abnormalities that required surgical correction (<5° tibiofemoral anatomic angle).²¹ None of the patients had ongoing concurrent orthopedic conditions or sensorimotor impairments that would affect their ability to participate in the study, as determined by their orthopedic specialist. Patients were referred directly to the study from participating orthopedic specialists who were aware of the inclusion and exclusion criteria; no patients declined to participate in the study. The mean age of patients was 38.6 years, the average height was 175.1cm, and mean body mass was 81.5kg. Ethics approval was obtained from the associated institutions and written informed consent from the participants was obtained before the onset of the study. A priori power calculation indicated a total sample size of 26 would reveal differences at the 1.7% significance level with a power of 0.8, using a moderate effect size of 0.6.

As part of a larger clinical trial being undertaken, patients were randomly assigned (block randomization, sex, and aged younger or older than 40y) to either traditional or accelerated load-bearing rehabilitation pathways. The traditional pathway consisted of a 5-week period of weight bearing at 20% (toe-touch) BW, followed by a progressive rise in load bearing until full weight bearing was attained at 11 weeks postsurgery. The accelerated load bearing gradient removed the initial 5-week toe-touch phase, whereby load bearing was progressively increased immediately with full weight bearing attained at approximately 8 weeks postsurgery (table 1). Only the accelerated group was subjected to a 40% BW weight-bearing stage (see table 1) and, for this reason, only 22 patients (the number of patients randomly assigned to the accelerated group) out of the total group of 48 underwent this weight-bearing condition (table 2). Assessment at 20% and 60% BW weight-bearing levels were still undertaken in both groups at the same point in the postoperative timeline (see table 1), but the accelerated patient group underwent the 80% BW weight-bearing level 2 weeks earlier than the traditional group (see table 1). Furthermore, as a result of the late introduction of the static weight-bearing assessment, only 18 patients completed static replication trials at 20% BW (see table 2). Finally, although 48 patients participated in this study, the number who participated in both the initial static and dynamic replication and the 7-day retention trials differed among the 20%, 40%, 60%, and 80% BW weight-bearing levels (see table 2). This was the result of either the research design or factors beyond our control, including illness and missed sessions.

Table 1. The Load Bearing Protocols for Both the Accelerated and the Traditional Patient Groups

Group	Weeks Postsurgery
	2	3	4	5	6	7	8	9	10	11	12
Traditional group
Weight bearing (%BW)	20	20	20	20	60	60	70	80	90	100	100
Test point number	20%A	20%B	NA	NA	60%A	60%B	NA	80%A	80%B	NA	NA
Crutches used	2	2	2	2	1	1	1	1	1	1	0
Brace	Y	Y	Y	Y	Y	Y	Y	Y	Y	Y	N
Accelerated group
Weight bearing (%BW)	20	30	40	50	60	80	100	100	100	100	100
Test point number	20%A	20%B	40%A	40%B	60%A	60B/80A	80%B	NA	NA	NA	NA
Crutches used	2	2	2	2	1	1	1	0	0	0	0
Brace	Y	Y	Y	Y	Y	Y	Y	N	N	N	N

NOTE. Patients were assessed immediately after instruction and practice (A) and 1 week after instruction (B).

Abbreviations: N, no; NA, not applicable; Y, yes.

Table 2. Summary of Expected and Actual Weight Bearing for Static, Initial Dynamic Replication, and 7-Day Retention Conditions Throughout 20%, 40%, 60%, and 80% Weight-Bearing Levels

Abbreviation: VAS, visual analog scale.

The bathroom scale method was used to train patients to follow the progressive weight-bearing program. This method involved patients placing their affected leg on the scales (accuracy, 0.1kg)^a with the unaffected leg next to the scales on a platform at the same height (fig 1). The patient performed 3 sets of 10 repetitions, ramping up to the nominated weight using the electronic scales as a visual guide. After this static loading practice, the patient walked for approximately 40m at the nominated PWB level and then returned to the scales to perform a final set of 10 static trials. All PWB practice and assessment was undertaken in bare feet to ensure standardization across all patients. At each postoperative stage, the patient was made aware of the PWB increment and of any changes with regard to the number of recommended walking aids. Patients wore a knee brace throughout all weight-bearing conditions and used 2 forearm walking aids at the 20% and 40% BW weight-bearing stages and 1 walking aid for the 60% and 80% BW weight-bearing stages as per the rehabilitation protocols. The PWB increment was calculated based on the current weight of the patient.

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• Fig 1. 

  With this load-bearing practice condition, the patient learns a new partial weight-bearing level on a set of scales to replicate that weight during walking.

Immediately after instruction and practice, we assessed patients on their ability to replicate the PWB force on the foot of the affected leg within 5% of BW in a static standing position and while walking. The 5% BW level was an arbitrary value chosen due to the large variation in weight-bearing replication accuracy⁸, ⁹, ¹⁰, ¹², ¹³, ¹⁴ reported using scales in the available literature, although the majority of available research on the use of scales reports accuracy not within 5% of BW.⁸, ⁹, ¹², ¹³, ¹⁴ Assessment was performed using a unidirectional forceplate (sampling rate, 500Hz) embedded in the center of a 5-m walkway to obtain the peak vertical ground reaction force loads. The vertical load recorded for each trial was the highest peak throughout the vertical ground reaction force curve regardless of whether it occurred at heel strike or push off.

Patients were initially assessed on their ability to replicate the PWB level (20%, 40%, 60%, 80% BW) in a static position. Patients were positioned with the affected leg over the forceplate and the unaffected leg next to the forceplate on the measuring platform (similar to that experienced during practice). The patient was asked to load the affected leg up to the nominated PWB level. A minimum of 5 practice trials in the static position were performed initially followed by 5 data collection trials with an average (± SD) of the peak vertical loads recorded.

After these static trials, we assessed the patients on their ability to dynamically replicate the PWB level during level walking. Patients were asked to ignore the forceplate and to walk as they would normally given their current stage of rehabilitation. The starting point for the patient was adjusted so that they made contact with the center of the forceplate without targeting and altering their walking gait. Once this had been achieved, the patient was permitted an additional 2 practice attempts for further familiarization, which were followed immediately by the data collection trials. The number of trials for each subject was not standardized; 3 adequate trials were required.²² Therefore, repeated efforts were often needed for the patient to strike the center of the forceplate with their affected leg on 3 occasions without making a conscious attempt to do so. A visual analog scale was administered to assess knee pain at the time of each assessment, whereby patients rated the frequency and severity of knee pain on a scale of 0 to 10 (see table 2).

Immediately after the last dynamic gait trial, we provided postresponse feedback on all static and dynamic replication trials for that session to patients that included the maximum weight produced for each trial undertaken and how far the patient was over or under the designated weight-bearing level. This protocol for dynamic replication was repeated 7 days later in a dynamic weight-bearing retention test.

We collected reaction force data through a custom-written LabView acquisition package^b and processed it with Microsoft Excel. The ground reaction force data were first filtered using a low-pass Butterworth filter with a 2.5-Hz cutoff frequency, which was selected using residual analysis and visual inspection.²³ The ground reaction force data were then normalized to 51 data points extending over the stance phase of the gait cycle. The level of weight bearing exerted by patients in both initial replication (static and dynamic) and follow-up retention trials (dynamic) were then converted and expressed as a percentage of patient BW (%BW) allowing comparison of actual and prescribed PWB levels.

A series of independent sample t tests was initially used to compare expected weight bearing with actual weight-bearing ability immediately after instruction in both static and dynamic conditions, and again dynamically 7 days later, throughout the selected target levels. Paired-sample t tests were used to analyze differences in dynamic weight-bearing ability immediately after instruction and 7 days later in the dynamic retention test. To adjust for these multiple comparisons, a Bonferroni correction was not used because this method is conservative, so statistical significance was determined at P less than .017 (ie, .05/3).²⁴ Furthermore, we used linear regression to investigate the strength of the relationship between static and dynamic weight-bearing replication error across the various weight-bearing conditions, whereas a Pearson correlation was used to assess the association between the 2 errors. The strength of Pearson correlations were defined as high, moderately high, moderate, low, or no relationship.²⁵ Analysis was performed using SPSS software.^c

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Results 

Despite differing patient numbers between the 3 weight-bearing conditions (static, immediate dynamic, 7-day dynamic retention), and across all weight-bearing levels, the average age and ratio of men to women was similar between all groups (see table 2). There was no difference in the frequency and severity of reported knee pain from immediate to 7-day retention testing or throughout the 4 different weight-bearing conditions (see table 2).

The 18 patients who completed initial static weight-bearing trials for the 20% BW weight-bearing level applied 12.9% BW more than the expected target, whereas the 22 patients who completed static weight-bearing replication trials for the 40% BW weight-bearing level applied 5.4% BW more than expected (see table 2, fig 2). The 43 patients completing static replication trials for the 60% BW weight-bearing level also applied 7.2% more than the expected target (see table 2, fig 2), whereas the 40 patients who completed initial static replication trials for the 80% BW weight-bearing level applied 0.4% less than expected (see table 2, fig 2). At least 58% of patients in each of the 4 weight-bearing conditions failed to maintain initial static weight-bearing within the 5% BW level, and no patient was within the 5% BW level for the 20% BW weight-bearing condition (table 3). At least 51% of patients in the 20%, 40%, and 60% BW weight-bearing trials failed to maintain static weight bearing within 10% of BW (see table 3).

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• Fig 2. 

  Although static replication of weight bearing (WB) was only significantly greater (P<.017) than expected for the 20% and 60% BW weight-bearing conditions, patients exerted more than 5% BW over the expected target for the 20%, 40%, and 60% BW weight-bearing trials. Patients were within 5% BW for the 80% BW weight-bearing static condition.

Table 3. The Percentage of Patients Within the ±5% and ±10% BW Limits for Static, Initial Dynamic Replication, and 7-Day Retention Conditions Across the 20%, 40%, 60%, and 80% Weight-Bearing Levels

The 41 patients who completed initial dynamic weight-bearing trials for the 20% BW weight-bearing level applied 15.8% BW more than the expected target during gait and the 22 patients who completed initial dynamic weight-bearing trials for the 40% BW weight-bearing level applied 8.3% BW more than expected (see table 2, fig 3). The 43 patients completing initial dynamic trials for the 60% BW weight-bearing level also applied 11.9% BW more than the expected target, although the 40 patients who completed initial dynamic replication trials for the 80% BW weight-bearing level applied 1.2% BW less than the expected target (see table 2, fig 3). At least 54% of patients in each of the 4 weight-bearing conditions failed to maintain initial dynamic weight bearing within the 5% BW level, and at least 58% of patients failed to maintain dynamic weight bearing within 10% of BW for the 20%, 40%, and 60% BW weight-bearing trials (see table 3).

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• Fig 3. 

  Immediate dynamic replication of weight bearing (WB) was significantly greater (P<.017), and more than 5% BW over the expected target for 20%, 40%, and 60% BW weight-bearing trials, but dynamic replication was within 5% BW for the 80% BW weight-bearing condition. Dynamic replication of weight bearing improved (P<.017) over a 7-day retest period for the 20% BW weight-bearing level only.

For the 7-day dynamic retention trials, patients exerted 6.6%, 4.2%, 9.9%, and 0.2% BW more than expected for the 20%, 40%, 60%, and 80% BW weight-bearing trials, respectively (see table 2, fig 3). At least 62% of patients within each of the 20%, 40%, and 60% BW weight-bearing conditions failed to maintain 7-day dynamic retention within 5% of BW, although at least 53% of patients within all 4 weight-bearing conditions were within 10% BW for the 7-day retention trials (see table 3).

There was a significant improvement (P=.004) in weight-bearing accuracy from initial to 7-day dynamic weight-bearing replication within the 20% BW weight-bearing trials, but we observed no differences across the 40%, 60%, and 80% BW weight-bearing conditions (see fig 3). Patient numbers in the 40% BW weight-bearing level were below our priori patient sample calculation of 26 (see table 2).

Pearson correlations between static and dynamic weight-bearing replication error revealed a moderately high relationship between replication errors in both static and dynamic conditions across all weight-bearing conditions (y=.70x+2.54, r=.74), whereas a high relationship was observed within the 20% (y=.88x+1.12, r=.94) and 40% (y=.73x+2.79, r=.85) BW weight-bearing levels alone (fig 4).

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• Fig 4. 

  Pearson correlations showed that patients who were poor at replicating weight-bearing (WB) restrictions statically were also poor at replication during gait, indicated by a moderately high relationship between static and dynamic weight-bearing replication error across all weight-bearing conditions. A high relationship existed within the 20% and 40% BW weight-bearing levels.

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Discussion 

A specific PWB program plays an essential role in providing both a protective and a progressive stimulus to developing chondrocytes after ACI.²⁶ It is therefore important for patients to closely replicate these graduated weight-bearing programs so that under- or overstimulation of the graft at any stage throughout the postoperative timeline does not occur, possibly hampering the attainment of best-quality tissue repair. Instruction and practice using a set of scales is a common and practical method of imposing these weight-bearing restrictions during walking.⁵, ⁸, ¹¹ However, differing success has been reported with the use of this technique,⁸, ⁹, ¹⁰, ¹², ¹³, ¹⁴, ¹⁷ the majority of the available literature revealing replication of weight bearing using scales outside 5% of BW.⁸, ⁹, ¹², ¹³, ¹⁴ Although this method has undergone trials in unaffected subjects⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁷, ¹⁸ and in patients after other orthopedic procedures,⁷, ⁹, ¹⁸ we know of no investigation in postoperative patients who have undergone ACI, in whom replication of weight bearing may be crucial to the protection, and development of repair tissue. Therefore, we sought to investigate whether patients undergoing ACI could replicate a series of nominated weight-bearing levels encountered throughout their postoperative weight-bearing rehabilitation program.

Our first hypothesis that patients were unable to replicate 20% (32.9% BW), 40% (45.4% BW), and 60% (67.2% BW) BW weight-bearing restrictions statically within 5% of BW immediately after practice and instruction using static loading was supported. Despite the overall mean for the static 80% BW weight-bearing condition being within 5% BW (79.6% BW), 58% of patients were still outside this limit, and 100% of patients who performed loading at the 20% level were outside the predicted 5% BW limit (see table 3). Accurate replication ability during the 20% BW weight-bearing stages after ACI is of particular importance, because they generally correspond with more crucial, earlier postoperative time points and, therefore, more potential for graft de-lamination. The inaccuracy reported is in contrast to Malviya et al¹⁰ who showed good static replication of a 25% BW weight-bearing restriction; however, only healthy, unaffected subjects were used.

Similar to the static weight-bearing condition, patients were unable to replicate loads of 20% BW (35.8% BW) during walking immediately after instruction (see table 2, fig 3), with 78% of patients outside the 5% BW limit (see table 2). These findings were similar to those reported in the literature,⁹, ¹⁴ wherein Dabke et al⁹ reported that 21 of 23 patients, after a range of orthopedic procedures, exerted a mean of 35.3% BW more than prescribed (20%–40% weight-bearing restriction) using the bathroom scale method. This inability to replicate low levels of weight bearing has also been observed in patients after total hip arthroplasty⁷ and surgical intervention to address lower-limb fractures.¹⁹ Patients failed to replicate weight-bearing levels of 40% (48.3% BW) and 60% (71.9% BW) BW during walking immediately after instruction (see fig 3). This finding is in contrast to Youdas et al¹² who showed good reproducibility of 50% PWB during walking in unaffected subjects using axillary and forearm walking aids after training on bathroom scales; however, only a small sample of healthy participants was used. In the current study, patients were accurate in replicating loads of 80% BW (78.8% BW) during gait possibly because 80% BW weight bearing is close to full weight bearing. Therefore, although weight-bearing accuracy during walking was within the 5% BW target cutoff for the 80% BW weight-bearing level, our second hypothesis was supported for the 20%, 40%, and 60% BW weight-bearing conditions.

Furthermore, patients failed to replicate weight-bearing levels of 20% (26.6% BW) and 60% (69.9% BW) BW during 7-day dynamic retention trials (see fig 3), which is again in contrast to previous findings.¹² In the current study, patients were accurate in replicating loads of 40% (44.2% BW) and 80% BW (80.2% BW) during walking in the 7-day retention condition. Therefore, although weight-bearing accuracy during walking was within the 5% BW target cutoff for the 40% and 80% BW weight-bearing levels, our third hypothesis was supported for the 20% and 60% BW weight-bearing conditions. Again, because the 20% BW weight-bearing condition corresponds with earlier and, therefore, more crucial postoperative time points, accurate replication ability should be of particular importance. It is yet unknown how overloading of the graft in the early stages (as was the case in the study) may affect long-term graft development.

Static weight-bearing practice using the bathroom scale method does not replicate the situation experienced during dynamic weight-bearing gait.⁸ Dynamic gait introduces outside influences in addition to BW, such as acceleration of the body and limbs. In addition, to simulate a walking surface, the measuring device must lie in the same plane as the walking surface. If not, the relative length of limbs and ambulatory aids changes.⁸ An attempt was made to overcome this issue by allowing the patient to support their nonaffected leg on a platform the same height as the scales (see fig 1). Furthermore, it must be acknowledged that the number of walking aids used varied depending on the level of weight-bearing restriction imposed as per the patients' rehabilitation program (ie, 2 crutches for 20% and 40% BW weight bearing, and 1 crutch for 60% and 80% BW weight bearing). Although the purpose of this study was to investigate weight-bearing ability given the designated weight-bearing protocols, rather than the effect that type and number of assistive devices has on weight-bearing ability, this may still influence the ability to weight bear between these different weight-bearing conditions.

Although age has been shown to affect weight-bearing accuracy,¹⁹ the average age, and ratio of men to women was similar between the different weight-bearing conditions, and across all weight-bearing levels. Therefore, the influence these factors had on weight-bearing accuracy differences between groups should have been negligible. Other factors that are often present in the postoperative patient who has undergone ACI, such as pain,⁹ reduced power,²⁰ an altered mental state, and fragility after the operative procedure, may also affect PWB ability. Therefore, the influence that each of these factors will have on the ability to follow weight-bearing restrictions will depend on each patient's physical and emotional strength, analgesic use, and tolerance to pain, as well as on the progression of pathologic parameters (ie, pain and joint effusion) through the early postoperative timeline. Knee joint effusion was not assessed in this study and it may have contributed to differences in weight-bearing ability, particularly in the early postoperative stages. However, knee pain before each trial was recorded and was constant from immediate replication to 7-day retention assessments and across all weight-bearing conditions (see table 2). Therefore, the influence knee pain had on the observed differences in weight-bearing accuracy across weight-bearing conditions should have been negligible.

There was no improvement in weight-bearing accuracy during walking between immediate and 7-day retention replication for the 40%, 60%, and 80% BW weight-bearing conditions, which supported our fourth hypothesis. However, patient numbers in the 40% BW weight-bearing level were below our priori patient sample calculation of 26, indicating that the sample may not have been large enough to detect significant changes. We observed an improvement for the 20% BW weight-bearing trials (see fig 3). Previous studies suggest that the effect of training in PWB may be limited, so that learning diminishes rapidly 1 to 2 days posttraining¹³, ¹⁷; however, some form of postresponse feedback may improve long-term learning.¹¹ The improvement in weight-bearing accuracy observed across the 7-day period for the 20% BW weight-bearing condition suggests that a quick and simple analysis of patient weight bearing (feedback) after practice trials may be beneficial in improving weight-bearing ability over 7 days, at least at low weight-bearing loads around 20% BW.

A moderately high relationship was observed between static and dynamic replication error across all weight-bearing conditions, and this association was high within 20% and 40% BW weight-bearing conditions (see fig 4), supporting our fifth hypothesis. This relationship observed between static and dynamic replication error suggests training should target those who have large static weight-bearing replication errors, particularly at low weight-bearing loads. Furthermore, the ability of patients to replicate the weight-bearing levels revealed low accuracy in replicating the lowest level target (20% BW) and better performance at the highest load (80% BW). Although these findings are both similar⁷, ⁹, ¹⁸, ¹⁹ and in contrast¹⁰, ¹² to those reported previously, it does suggest more emphasis should be placed on training the lower PWB levels.

Study Limitations 

Although a graduated weight-bearing program is believed to provide protection and progressive stimulation to the developing chondrocytes after ACI, optimal protocols have yet to be established. For this reason, the result of patients' inability to replicate desired weight-bearing levels on the short- and long-term outcome of repair tissue after ACI is unknown. Our study did not address the biologic outcome of repair tissue after under- or overloading of external weight bearing throughout the postoperative program but rather the patient's ability to replicate these weight-bearing restrictions. Furthermore, we acknowledge that more time spent practicing PWB may prove beneficial in accuracy of replication during gait. However, the level of instruction and practice performed in the current study corresponds to that which may be routinely provided, whereas anything more may not be practical in a clinical setting.

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Conclusions 

Patients undergoing ACI were unable to replicate static and dynamic weight-bearing restrictions of 20%, 40%, and 60% BW within 5% of BW after practice and instruction using the bathroom scale technique. These results are both comparable and in contrast to those reported in the literature; however, research has focused on unaffected subjects⁸, ⁹, ¹⁰, ¹¹, ¹², ¹³, ¹⁷, ¹⁸ and patients with other orthopedic procedures.⁷, ⁹, ¹⁹ Patients were accurate in replication of the high weight-bearing loads (ie, 80% BW) but were inaccurate with the low weight-bearing loads (ie, 20% BW). This early stage corresponds with a more crucial point in the postoperative timeline, and for this reason more emphasis should be placed on training these lower weight-bearing levels. Furthermore, patients who showed greater static replication error displayed greater replication error during gait and, therefore, should the rehabilitation facility not have easy access to a dynamic force platform, the patient may marginally benefit from extra time spent practicing static PWB on a set of bathroom scales. These findings can be used to improve weight-bearing instruction protocols and patient accuracy throughout rehabilitation after other lower-limb orthopedic procedures for which weight-bearing restrictions should be followed. Furthermore, future research should be directed at how long-term graft development may be affected by weight-bearing inaccuracy (and in particular overloading), especially in the crucial early stages after ACI, as well as by differing postoperative weight-bearing protocols.

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References 

1. Brittberg M, Lindahl A, Nilsson A, Ohlsson C, Isaksson O, Peterson L. Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation. N Engl J Med. 1994;331:889–895
   • View In Article
   • MEDLINE
   • CrossRef
2. Gillogly SD, Voight M, Blackburn T. Treatment of articular cartilage defects of the knee with autologous chondrocyte implantation. J Orthop Sports Phys Ther. 1998;28:241–251
   • View In Article
   • MEDLINE
3. Peterson L, Minas T, Brittberg M, Nilsson A, Sjogren-Jansson E, Lindahl A. Two- to 9-year outcome after autologous chondrocyte transplantation of the knee. Clin Orthop Relat Res. 2000;(374):212–234May
   • View In Article
4. Ronga M, Grassi FA, Bulgheroni P. Arthroscopic autologous chondrocyte implantation for the treatment of a chondral defect in the tibial plateau of the knee. Arthroscopy. 2004;20:79–84
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (349 KB)
   • CrossRef
5. Hambly K, Bobic V, Wondrasch B, Van Assche D, Marlovits S. Autologous chondrocyte implantation postoperative care and rehabilitation: science and practice. Am J Sports Med. 2006;34:1–19
   • View In Article
6. In:  Robertson WB,  Gilbey H,  Ackland T editor. Standard practice exercise rehabilitation protocols for matrix induced autologous chondrocyte implantation femoral condyles. Perth: Hollywood Functional Rehabilitation Clinic; 2004;
   • View In Article
7. Hurkmans HL, Bussmann JB, Selles RW, Benda E, Stam HJ, Verhaar JA. The difference between actual and prescribed weight bearing of total hip patients with a trochanteric osteotomy: long-term vertical force measurements inside and outside the hospital. Arch Phys Med Rehabil. 2007;88:200–206
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (3304 KB)
   • CrossRef
8. Gray FB, Gray C, McClanahan JW. Assessing the accuracy of partial weight-bearing instruction. Am J Orthop. 1998;27:558–560
   • View In Article
9. Dabke HV, Gupta SK, Holt CA, O'Callaghan P, Dent CM. How accurate is partial weightbearing?. Clin Orthop Relat Res. 2004;(421):282–286Apr
   • View In Article
10. Malviya A, Richards J, Jones RK, Udwadia A, Doyle J. Reproducibility of partial weight bearing. Injury. 2005;36:556–559
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (70 KB)
    • CrossRef
11. Winstein CJ, Pohl PS, Cardinale C, Green A, Scholtz L, Waters CS. Learning a partial-weight-bearing skill: effectiveness of two forms of feedback. Phys Ther. 1996;76:985–993
    • View In Article
    • MEDLINE
12. Youdas JW, Kotajarvi BJ, Padgett DJ, Kaufman KR. Partial weight-bearing gait using conventional assistive devices. Arch Phys Med Rehabil. 2005;86:394–398
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (164 KB)
    • CrossRef
13. Warren CG, Lehmann JF. Training procedures and biofeedback methods to achieve controlled partial weight bearing: an assessment. Arch Phys Med Rehabil. 1975;56:449–455
    • View In Article
    • MEDLINE
14. Li S, Armstrong CW, Cipriani D. Three-point crutch walking: variability in ground reaction force during weight bearing. Arch Phys Med Rehabil. 2001;82:86–92
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (94 KB)
    • CrossRef
15. Gapsis JJ, Grabois M, Borrell RM, Menken SA, Kelly M. Limb load monitor: evaluation of a sensory feedback device for controlled weight bearing. Arch Phys Med Rehabil. 1982;63:38–41
    • View In Article
    • MEDLINE
16. King PS, Gerhardt JJ, Pfeiffer EA, Usselman LB, Fowlks EW. System for controlling ambulation pressure (SCAP-3) in patients with disabilities of the lower extremity. Am J Phys Med. 1972;51:9–15
    • View In Article
    • MEDLINE
17. Tveit M, Karrholm J. Low effectiveness of prescribed partial weight bearing (Continuous recording of vertical loads using a new pressure-sensitive insole). J Rehabil Med. 2001;33:42–46
    • View In Article
    • MEDLINE
    • CrossRef
18. Krause D, Wunnemann M, Erlmann A, et al. Biodynamic feedback training to assure learning partial load bearing on forearm crutches. Arch Phys Med Rehabil. 2007;88:901–906
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (334 KB)
    • CrossRef
19. Vasarhelyi A, Baumert T, Fritsch C, Hopfenmuller W, Gradl G, Mittlmeier T. Partial weight bearing after surgery for fractures of the lower extremity—is it achievable?. Gait Posture. 2006;23:99–105
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (240 KB)
    • CrossRef
20. Chow SP, Cheng CL, Hui PW, Pun WK, Ng C. Partial weight bearing after operations for hip fractures in elderly patients. J R Coll Surg Edinb. 1992;37:261–262
    • View In Article
    • MEDLINE
21. Robertson WB, Fick D, Wood DJ, Linklater JM, Zheng MH, Ackland TR. MRI and clinical evaluation of collagen-covered autologous chondrocyte implantation (CACI) at two years. Knee. 2007;14:117–127
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (842 KB)
    • CrossRef
22. Hughes J, Clark P, Klenerman L. The importance of the toes in walking. J Bone Joint Surg Br. 1990;72:245–251
    • View In Article
    • MEDLINE
23. Winter D. Biomechanics and motor control of human movement. 2nd ed. New York: John Wiley; 1990;
    • View In Article
24. Smith AJ, Lloyd DG, Wood DJ. Pre-surgery knee joint loading patterns during walking predict the presence and severity of anterior knee pain after total knee arthroplasty. J Orthop Res. 2004;22:260–266
    • View In Article
    • MEDLINE
    • CrossRef
25. Safrit M. Introduction to measurement in physical education and exercise science. St Louis: Times Mirror/Mosby College Publishing; 1986;
    • View In Article
26. Willers C, Wood D, Zheng MH. A current review on the biology and treatment of articular cartilage defects (parts I & II). J Muscoskel Res. 2003;7:157–181
    • View In Article

• a Electronic Wedderburn scales; Tanita Corp, 2625 S Clearbrook Dr, Arlington Heights, IL 60005.
• b LabView version 7.1; National Instruments Corp, 11500 N Mopac Expy, Austin, TX 78759.
• c Version 11.5; SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.