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High Rate of Failure of Allograft Reconstruction of the Extensor Mechanism After Total Knee Arthroplasty*

MAJOR SETH S. LEOPOLD, , UNITED STATES ARMY MEDICAL CORPS, NELSON GREIDANUS, M.D., WAYNE G. PAPROSKY, M.D., RICHARD A. BERGER, M.D. and AARON G. ROSENBERG, M.D.CHICAGO, ILLINOIS

Investigation performed at the Department of Orthopaedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, Chicago

	Abstract

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Background: Disruption of the extensor mechanism is an uncommon but devastating complication of total knee arthroplasty. Several techniques for reconstruction of the extensor mechanism after total knee arthroplasty have been reported, but we do not know of any study in which the results of one group's method were corroborated by a second group using the same technique. In the present series, we evaluated the results of reconstruction of the extensor mechanism with use of allograft according to the method described by Emerson et al. Methods: Seven reconstructions of the extensor mechanism with use of a bone-tendon-bone allograft were performed with the technique of Emerson et al. in six patients. The patients were evaluated before and after the operation. The knee score according to the system of The Hospital for Special Surgery, evidence of an extensor lag, use of walking aids, and the ambulatory status of each patient were recorded. The patients were also asked about, and the medical records were reviewed for, episodes of falling related to weakness of the quadriceps after the reconstruction. The mean duration of follow-up was thirty-nine months (range, six to 115 months). As these reconstructions often fail early, the minimum duration of follow-up was six months. Results: All seven reconstructions were rated as clinical failures on the basis of a persistent or recurrent extensor lag of more than 30 degrees. All but one patient needed an assistive device full time for walking, and four patients (five knees) had at least one documented episode of falling that was due to giving-way of the affected knee. Four of the reconstructions were revised; one revision was performed with use of another extensor mechanism allograft and three were performed with use of a medial gastrocnemius rotation flap. The other three clinical failures had not been revised at the time of writing. At the time of the most recent follow-up (or at the time of revision of the extensor reconstruction), the mean extensor lag was 59 degrees and the mean knee score was 52 points (a poor result). Conclusions: Undertensioning of the allograft reconstruction at the time of the operation and attenuation of the allograft both may have played a role in the inability of the patients to regain active extension of the knee postoperatively. Alternative techniques for reconstruction of the extensor mechanism or modifications of this technique should be considered in the treatment of this difficult problem.

	Introduction

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The prevalence of disruption of the extensor mechanism after total knee arthroplasty reportedly has been as high as 2.5 percent (seven of 281)⁹. Treatment of this catastrophic complication with use of primary direct repair or a xenograft was associated with failure in eleven of seventeen knees in the largest series¹³ reported to date as far as we know. Better results have been reported after three other operative techniques: reconstruction with autogenous semitendinosus tendon², reconstruction with a medial gastrocnemius muscle transposition flap⁷, and reconstruction with an extensor mechanism allograft^4,5. Booth et al.¹ also recently reported promising results after an operative technique that involved use of an extensor mechanism allograft but that differed in an important way from a previously described technique^4,5 because they incorporated a change in the manner in which the graft is tensioned when it is attached to the quadriceps tendon. We know of no study to date in which the results of one group's method were corroborated by a second group using the same technique.

Emerson et al.⁴ reported encouraging initial results in a group of thirteen knees that had been treated with an allograft consisting of tibial tubercle, patellar ligament, patella, and quadriceps tendon to repair a rupture of the patellar ligament that had occurred during or after total knee arthroplasty. They found reliable osseous union at the junction of the distal allograft bone plug (at the inferior portion of the allograft patellar ligament) and the host tibial tubercle, and no patient had an extensor lag of more than degrees. However, a subsequent follow-up examination of the same group revealed that three of the nine knees that had been followed for at least two years had an unacceptable extensor lag of 20, 25, or 40 degrees⁵. Nevertheless, Emerson et al.⁵ concluded that the procedure remained an option for elderly patients who place low demands on the knee. The purpose of the present study was to determine whether the modest success achieved by Emerson et al.^4,5 could be reproduced with use of allograft to reconstruct a disrupted extensor mechanism after total knee arthroplasty.

	Materials and Methods

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Criteria for Inclusion
From 1989 through 1998, seven consecutive reconstructions of the extensor mechanism were performed by our group in six patients who had had a total knee arthroplasty. These patients were entered prospectively into our study and were followed for a minimum of six months. The short duration of follow-up was selected because this procedure often fails in the early postoperative period. Allograft reconstruction with the technique of Emerson et al.^4,5 was the only method that we used during the period of the study to treat disruption of the extensor mechanism after total knee arthroplasty. One of the patients had two reconstructions performed in the same knee. Both of those reconstructions are included in the present study because, at the time of the second procedure, the method of Emerson et al. was the only reported technique of which we were aware that could be used to treat a complete disruption of the extensor mechanism.

All of the knees in the present series had had multiple previous operations, and three had had a failed previous attempt to salvage a disrupted extensor mechanism. The previous reconstructions in those three knees included one direct repair and one reconstruction with an autogenous semitendinosus graft², both of which were performed at outside institutions. The third knee had a second extensor mechanism allograft (as already mentioned) when the initial reconstruction failed because of nonunion of the tibial tubercle.

Six of the seven reconstructions of the extensor mechanism were performed as part of a revision arthroplasty (defined as an exchange of at least one prosthetic component). The remaining operation was performed as an isolated procedure without revision of any knee components.

Data on the Patients and Clinical End Points
Prospective data with regard to pain, function, use of walking aids (a cane, crutch, walker, or brace), range of motion, and extensor lag were gathered for each patient both before and after the operation. The extensor lag was calculated by subtracting the maximum extension that the patient could achieve actively against gravity from the maximum passive extension of the knee. The extensor lag and the range of motion were measured with use of a handheld goniometer by an examiner other than the operating surgeon. At the latest follow-up examination, an independent examiner other than the operating surgeon used the same end points to evaluate the patients. The knee also was graded according to the 100-point system of The Hospital for Special Surgery⁶ both before and after the operation. A score of 85 points or more is considered an excellent result; 70 to 84 points, a good result; 60 to 69 points, a fair result; and less than 60 points, a poor result.

As quadriceps weakness in elderly individuals is associated with an increased risk of falling⁸, all patients were questioned and the charts were reviewed to determine how many patients had fallen, once or several times, after the reconstruction of the extensor mechanism.

As the procedure under study is performed to improve active extension of the knee, we defined clinical failure as an extensor lag of more than 30 degrees.

Operative Technique
The allograft reconstruction of the extensor mechanism was performed with the technique of Emerson et al.^4,5. Those authors outlined six general principles of operative technique, which were strictly followed in the present series. First, no host tissue should be removed in the process of inserting the allograft (scar tissue may be resected from the knee as needed for exposure for revision arthroplasty). Second, the host-allograft junctions at the quadriceps tendon and at the tibial tubercle should be as secure as possible; rigid internal fixation should be used for the tibial tubercle, and interrupted, heavy, nonabsorbable suture should be used for the quadriceps anastomosis. While the anastomosis is being sutured, the allograft patella should be maintained in the appropriate position on the femoral component throughout the range of motion. Third, the allograft should be balanced and tensioned to obtain smooth patellar tracking and full extension of the knee. Fourth, the allograft should be covered with as much autogenous tissue as possible. Fifth, the allograft should not be damaged during preparation. Finally, healthy skin flaps should be maintained and no tension should be put on the skin closure.

We used the specific technique described by Emerson et al.^4,5. First, the allograft tibial tubercle was keyed into place anatomically or slightly medially in the proximal part of the tibia to improve patellar tracking. Interference fit was generally achieved, and fixation was augmented with use of screws with or without supplemental tension-band wiring. Patellar height was set by resting the patella in the anterior flange of the femoral component. The anastomosis of the quadriceps was performed with use of heavy, nonabsorbable suture; the allograft tendon was attached to the host quadriceps tendon to optimize the medial-lateral pull of the quadriceps and to keep the patella from tilting with flexion. The quadriceps muscle, with the allograft in place, was sutured under slight tension with the knee fully extended. When this had been done, a variable amount of flexion, ranging from 40 to 80 degrees and depending on the soft-tissue compliance and the body habitus of the patient, could be attained intraoperatively with use of gravity only. This amount of flexion was in the range of the 60 degrees recommended by Emerson et al. in the initial report on the technique⁴. To optimize healing, the allograft was placed under as much host tissue as possible.

The allograft segments were all fresh-frozen, nonirradiated specimens consisting of tibial tubercle, patellar ligament, and patella with a generous amount of attached quadriceps tendon, which allowed for a broad area of contact between the graft and the host at the level of the quadriceps anastomosis.

The allograft patellae were not resurfaced in the present series.

Loose or unstable arthroplasty components were revised and the extensor mechanism was reconstructed during the same operative procedure.

Postoperative Management
All patients wore a brace with the knee in extension for six to eight weeks. During that time, isometric quadriceps exercises were performed under the supervision of a physical therapist. Toe-touch weight-bearing was permitted until radiographs showed incorporation of the tibial tubercle portion of the allograft, at which time full weight-bearing was permitted. After six to eight weeks, a progressive active range of flexion was permitted with use of a hinged brace while the quadriceps-strengthening exercises were continued.

Statistical Analysis
The paired two-tailed t test was performed to assess differences between preoperative and postoperative end points.

	Results

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No patient was lost to follow-up, which averaged thirty-nine months (range, six to 115 months). The mean age at the time of the operation was seventy-three years (range, sixty-two to eighty-two years).

Preoperatively, the mean extensor lag was 67 degrees (range, 25 to 95 degrees), the mean knee score was 50 points (range, 25 to 70 points), and the mean maximum active flexion was 103 degrees (range, 95 to 120 degrees). Before the reconstruction, one patient was able to walk about the community for an unlimited distance with use of a walker, two patients were able to walk a limited distance with use of a walker and the assistance of another person, two patients (three knees) were able to walk in the house with use of a walker, and one patient was not able to walk (Table I).

Four patients (five knees) had at least one episode of falling that was documented in the medical records and was severe enough to cause the patient to seek medical attention; one other patient, when questioned on the subject, described multiple falls. All of the falls occurred after the reconstruction and seemed to be related to giving-way of the knee as a result of an inability to maintain active extension of the knee during stance.

Four of the six patients indicated that they were satisfied with the procedure because of the decrease in pain and despite an inability to walk without supports or despite a back-knee gait. The relief of pain may have been a result of the revision arthroplasty rather than of the reconstruction of the extensor mechanism; six of the seven procedures had included a revision total knee arthroplasty as well as the reconstruction of the extensor mechanism.

Four of the reconstructions were revised. At the revision, three knees were found to have attenuation and stretching of the graft (two involved the allograft quadriceps tendon and one, the allograft patellar ligament) and one had rupture of the allograft patellar ligament. In both knees that had attenuation of the quadriceps tendon portion of the allograft, the suture line was examined and found to be intact, which indicated that dehiscence had not occurred at the anastomosis. Such examination was possible because heavy, nonabsorbable suture had been used for the anastomosis. Physical and radiographic examinations indicated that the other three clinical failures, which had not been revised at the time of writing, included rupture of the quadriceps tendon, nonunion of the tibial tubercle, and an extensor lag in one knee that had no palpable defect in the patellar ligament or the quadriceps tendon and that had radiographic union at the tubercle and an intact allograft patella. In that knee, the extensor lag had developed progressively during the first postoperative year but had not been present when the patient was examined in the early postoperative period. This mechanism of failure also is suggestive of attenuation of the allograft tissue.

One knee was revised with use of another extensor mechanism allograft, which was the only reported technique for reconstruction of a completely deficient extensor mechanism that we knew of at that time. That reconstruction later failed, and the patient had reconstruction with use of an extended medial gastrocnemius transposition flap⁷. Two other failed reconstructions were revised with use of a medial gastrocnemius muscle rotation flap. All three of these patients had substantial improvement in extensor function as well as in the ability to walk, and the extensor lag measured 0, 15, and 25 degrees at the time of the latest follow-up. However, as the duration of follow-up was less than one year at the time of writing, we cannot comment definitively on the effectiveness of that procedure. Except for the revisions, no repeat operations were performed in this series.

	Discussion

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The present study is the first, to our knowledge, in which an attempt was made to reproduce the results of reconstruction of the extensor mechanism with use of allograft tissue according to the technique of Emerson et al.^4,5. Because we were evaluating the results of a defined procedure, it is important to identify any differences between the previously reported technique and the methods that we used. As previously indicated, the operative principles and specific methods of Emerson et al.^4,5 were followed carefully. In particular, positioning and tensioning of the graft, fixation of the tibial tubercle, quadriceps anastomosis, and careful soft-tissue technique were performed exactly as described in the reports by Emerson et al.^4,5.

Some elements of the technique described by Emerson et al.^4,5 evolved over the course of those studies. Although they had used both freeze-dried and fresh-frozen allografts in those studies, Emerson et al. came to recommend fresh-frozen allografts because of issues associated with the durability of the freeze-dried grafts. All patients in the present report received fresh-frozen, nonirradiated allografts. Emerson et al.^4,5 reported a high rate of patellar complications associated with resurfacing of the allograft patella. In fact, they concluded that "eliminating the [patellar] prosthesis may not diminish the clinical results and may add to the durability of the construct."⁵ On the basis of that recommendation and the fact that the allograft patella is insensate, we did not resurface the patella in the present series. Finally, in order to maximize the likelihood of healing at the host-allograft soft-tissue junction at the quadriceps anastomosis, the knee was immobilized in extension for six to eight weeks postoperatively; this rehabilitation protocol is somewhat more conservative than that used by Emerson et al.^4,5, who allowed early motion at three weeks.

Emerson et al. reported restoration of full active function of the quadriceps (no extensor lag) in six of nine patients at a mean of 4.1 years after allograft reconstruction of an extensor mechanism that had ruptured after total knee arthroplasty⁵. Two of the other three patients had a minor extensor lag (less than 30 degrees) at the time of the latest follow-up. The mean knee score for the nine patients improved to 78 points. Even more impressive was the fact that five of the nine patients walked without an assistive device, three needed a cane, and only one needed a walker. Emerson et al. reported a number of complications related to the procedure, including wound dehiscence, rupture of the graft, and loosening of the patellar component. However, they concluded that the procedure can be useful for elderly patients who place low demands on the knee, although their data did not demonstrate a difference in the rate of survival or function of the graft on the basis of age or activity level⁵.

Our experience with the technique was not as gratifying as that of Emerson et al.^4,5. No discernible functional improvement was seen at a mean of thirty-nine months. Five of the six patients still used an assistive device full time, and four of them (five knees) needed a walker in order to walk at all. We detected no significant improvement in the extensor lag or the knee score, with the numbers available. The absence of significant differences between the preoperative and follow-up values could be a reflection of the small sample size (low statistical power). However, even more important was our conclusion that the results of the procedure—whether significant or not—were not clinically satisfactory. Episodes of falling because of quadriceps weakness occurred after five of the seven reconstructions, and four reconstructions of the extensor mechanism had to be revised. Three of these revisions were performed with a medial gastrocnemius rotation flap^7,10, and, although they were followed for less than one year, all three resulted in substantial restoration of active extensor power and none resulted in an extensor lag of more than 30 degrees.

Despite these complications, four of the six patients expressed satisfaction with the procedure when asked. It seems likely that their satisfaction was related to a decrease in pain, which, in turn, was largely the result of revision of a loose, unstable, or malaligned prosthesis.

There have been reports of patients who did not have the quadriceps muscle group having a stable gait, even after joint arthroplasty^3,11,12. However, weakness or dysfunction of the extensor mechanism has been identified as an important predictor of falling by the elderly⁸. The gait adaptations needed for walking with an incompetent extensor mechanism, including hyperextension of the knee and abnormal muscle forces, dramatically increase the stresses on a knee replacement¹⁴. These abnormal forces can lead to failure and loosening of the prosthesis as well as stress fractures³. For these reasons and others, disruption of the extensor mechanism after total knee arthroplasty is considered a devastating complication^2,4,7.

Therefore, restoration of active extension should be considered an important and independent end point for the assessment of the success of reconstructions of this type, regardless of improvements in scores for pain. As all of our patients had a persistent, severe lack of active extension, we concluded that the results of this procedure were not satisfactory.

There may be several explanations for these unsatisfying results. Emerson et al. stated that extensor lag is "primarily a technical problem with quadriceps retensioning."⁵ This seems to be a reasonable explanation for an extensor lag that is seen immediately or shortly after discontinuation of postoperative immobilization and use of a brace. This theory apparently is supported by the findings of a preliminary study on extensor mechanism allografts by Booth et al.¹, who noted that the rate of failure was lower when the operative technique had been modified to include suturing of the quadriceps anastomosis with the knee in full extension and the graft under maximum tension. The results of that study, with respect to the ability to walk, the knee score, and the extensor lag, were excellent. It is worth noting that, although Booth et al.¹ used allograft tissue for reconstruction of the extensor mechanism, their method for tensioning of the graft and their rehabilitation protocol were substantially different from those used by Emerson et al.⁴. Those investigators⁴ allowed approximately 60 degrees of flexion of the knee intraoperatively "without excessive tightness," and they allowed flexion of the knee immediately after the operation; Booth et al. performed the anastomosis of the quadriceps with the knee in extension and the graft under maximum tension, and they immobilized the knee in an extension brace postoperatively¹. Because of these important differences in technique, the method recently described by Booth et al.¹ should not be considered a reproduction of the original method^4,5. In fact, as far as we know, except for the investigators who described the procedures, no one has reported on a clinical series in which any of the three techniques for reconstruction of the extensor mechanism after total knee arthroplasty (use of an allograft^4,5, semitendinosus autogenous graft², or gastrocnemius flap⁷) had been used.

However, it is not obvious how undertensioning of the graft can account for progressive lag after a period of good extensor function. Indeed, attenuation of the graft, which certainly would not be prevented by tensioning the graft more tightly, was documented at the revision operation in three of the four knees that were revised in our series, and it was probably the mechanism of failure in a patient in whom a progressive lag developed late in the first postoperative year, after the knee had earlier regained full active extension. Likewise, the other mechanisms of failure, including rupture of the patellar ligament, rupture of the quadriceps tendon, and nonunion of the tibial tubercle, would not be caused by undertensioning of the graft. In their more recent report, Emerson et al.⁵ paid greater attention to the preparation of the soft-tissue envelope, including the use of soft-tissue expanders, local rotation flaps, and even free flaps to improve the vascularity of the tissue and the likelihood of a durable result, before the allograft reconstruction.

As already mentioned, the site of failure of the reconstructions was neither consistent nor predictable. In addition to the soft-tissue failures, one knee had nonunion of the tibial tubercle. The high rate of union at the tibial tubercle allograft-host junction (six of seven knees) in the present study is consistent with that in previous reports^1,4,5, which documented reliable fixation at that junction. In the present report, there were no failures related to the patella itself; in contrast, patellar failures were prominent in the series of reconstructions with an allograft extensor mechanism reported by Emerson et al.^4,5. However, as the early technique included resurfacing of the allograft patella, many of the patellar failures were related to loose or worn patellar components. Thus, Emerson et al.⁵ concluded that it is preferable not to resurface the allograft patella. Because we believed, as they did, that the allograft patella is insensate, we did not perform patellar resurfacing in our patients.

In summary, use of allograft tissue according to the technique of Emerson et al.^4,5 for reconstruction of the extensor mechanism after total knee arthroplasty was associated with a high rate of failure in the present small series of patients. Failure resulted in a progressive extensor lag and the need for full-time use of an assistive device in order to walk or the development of a compensatory back-knee gait. Episodes of falling because of weakness of the quadriceps were common and potentially dangerous. Improvements in intraoperative tensioning, perhaps by suturing the graft as tightly as possible with the knee in full extension¹, may reduce the number of failures of this procedure, but alternative techniques for reconstruction of the extensor mechanism or modifications of the technique of Emerson et al.^4,5 may be worth considering^1,2,7.

	Footnotes

 
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

The views expressed in this article are those of the authors and do not reflect the official policy of the United States Department of Defense or the United States Government.

Orthopaedic Surgery Service, William Beaumont Army Medical Center, 5005 North Piedras Street, El Paso, Texas 79920-5001.

Department of Orthopaedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, 1725 West Harrison Street, Suite 1063, Chicago, Illinois 60612.

	References

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2. Cadambi, A., and Engh, G. A.: Use of a semitendinosus tendon autogenous graft for rupture of the patellar ligament after total knee arthroplasty. A report of seven cases. J. Bone and Joint Surg., 74-A: 974-979, Aug. 1992.
3. Capanna, R.; Ruggieri, P.; Biagini, R.; Ferraro, A.; DeCristofaro, R.; McDonald, D.; and Campanacci, M.: The effect of quadriceps excision on functional results after distal femoral resection and prosthetic replacement of bone tumors. Clin. Orthop., 267: 186-196, 1991.
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