Patients with and without concurrent osteotomies experienced improvements (p < 0.001) in all functional scores. There were no substantial differences between patients without osteotomies and individual subgroups of patients with isolated tibial tubercle osteotomy (TTO) (p values ranged from 0.16 to 0.23 for the different functional scores), or a combination of TTO and high tibial osteotomy (HTO) (p values, 0.09 to 0.16); differences were small in comparison with a group of patients with isolated HTO (p values, 0.04 to 0.13). Comparing patients with HTO and patients who had undergone TTO demonstrated better outcomes for the HTO group at final followup (Table 5) when considering absolute levels; however, TTO patients started with worse scores.
Subsequent surgical procedures (SSP) after the index implantation were performed in 95 of the 155 knees (61%), the majority (52 of 95) for periosteal hypertrophy. Other indications included arthrofibrosis (32 of 95), graft complications (23 of 95), and periosteal delamination (11 of 95), with several patients having more than one diagnosis treated during a SSP. Graft complications were partial graft delamination, affecting less than 20% of the defect area, in 21 knees, treated with arthroscopic interventions, either microfracture (eight), abrasion arthroplasty (five) or OATS (eight). None of the patients undergoing a subsequent surgical procedure went on to complete failure requiring joint replacement.
Large, multiple, and bipolar cartilage defects represent an early stage in the wide spectrum of disease termed osteoarthritis. Treatment options for these patients are controversial since many are too young for joint replacement, yet cartilage repair such as ACI has traditionally been contraindicated for these degenerative lesions. The purpose of this study was to (1) report on the overall failure rate, as defined by revision with arthroplasty, of ACI in a population of young patients with early osteoarthritic changes; (2) describe the functional outcomes seen with this procedure; (3) investigate potential differences in patients requiring concurrent osteotomies; and (4) provide an overview of subsequent surgical procedures that become necessary after ACI.
Our study has several limitations. First, observational case series without a control group are subject to the effects of potential confounding factors that may either obscure a relationship or suggest an association where none actually exists. Second, most of our patients presented to us specifically to avoid or postpone knee arthroplasty; a randomized controlled study comparing cartilage repair with arthroplasty, while important, was therefore not feasible in our patient population. Our patients, on average, had previously undergone between two and three unsuccessful procedures directed at cartilage repair, such as débridement, chondroplasty, or marrow stimulation. They were therefore not agreeable to randomization for a study of ACI versus such techniques, which they had already failed in the past. Third, the indications of ACI and other cartilage repair procedures, especially microfracture, do not overlap, complicating the design of a randomized study: due to its invasiveness, ACI should be reserved for larger lesions above 4 cm2, whereas microfracture is indicated for smaller lesions. We believe, however, that in the absence of randomized data, observational studies can provide important information on outcomes of specific procedures. Further, our study was prospective and the followup data were collected by observers other than the surgeon, we used numerous validated instruments to measure clinical outcomes, the followup response rate was high, and there was minimal variability in treatment technique and rehabilitation protocols due to the single-surgeon experience. Finally, the term osteoarthritis is used to describe a wide spectrum of disease, ranging from localized chondral damage to complete loss of joint space. There is also controversy whether osteoarthritis is a disease affecting the cartilage, or a disease of the entire joint, including the subchondral bone and synovial lining. We chose our definition of early OA based on the radiographic criteria.
Young patients with early arthritic changes present a challenging problem and treatment with joint arthroplasty is frequently recommended. Primary total (TKR) or unicompartmental (UKR) knee arthroplasty provides excellent pain relief with patient satisfaction ranging between 73% and 85% in older patient age groups [5, 11, 28, 48]. Large implant survival studies drawn from joint registry programs have demonstrated 10-year survival rates of 60% to 70% for partial knee arthroplasties and 80% to 90% for total knee arthroplasties [25, 33]. Younger patients seem less satisfied with the outcome and also demonstrate higher implant failure rates . In a report on knee arthroplasty in patients younger than 40 years, a group comparable to the one presented in our study, the authors noticed good and excellent Knee Society function scores in only 50% of patients and a revision rate of 12.5% at 8 years . The subsequent revision surgeries, all but guaranteed within the lifetime of this young patient group, have an even more guarded prognosis: increasingly complex, these procedures result in progressively compromised outcomes [19, 56], and patient satisfaction after revision knee arthroplasty has been reported as low as 59% . Furthermore, prosthesis survival time is lessened: in younger patients (< 65 years), 5-year survival as low as 82% has been reported in a large registry study focused on revision knee arthroplasty . Lastly, revision surgery is extremely costly, with average charges of $73,000 in a recent study . It therefore seems reasonable to attempt delaying arthroplasty as long as possible in young patients, utilizing nonoperative measures such as physical therapy, antiinflammatories and injections, followed by limited surgical measures such as arthroscopic chondroplasty. A subset of patients, however, fails to experience pain relief with these measures and require more invasive interventions, such as cartilage repair with ACI for large, degenerative lesions, as presented here.
Eight percent (12 of 155) of knees treated with ACI met the criteria of treatment failure at an average of 64 months as defined by revision with partial or total knee arthroplasty; six of these patients received payments through worker's compensation (WC), resulting in a failure rate of 27.3% (six of 22) in that subgroup. ACI in non-WC patients failed at a rate of 4.5% (six of 133). The definition of failure for this study was limited to revision by arthroplasty: patients in this group usually presented to our office to avoid arthroplasty, which the majority had previously been recommended; we therefore wanted to measure our success in avoiding this outcome. We have used a more stringent definition of failure in the past, which includes any open revision surgery, including repeat cartilage repair with ACI or osteochondral allograft. Based on this more stringent definition, our failures would include two additional joints, which were successfully revised with repeat ACI, for a total failure rate of 9% (14 of 155). Bipolar (kissing) lesions have long been considered particularly challenging and are considered a contraindication to ACI by some. Of the 42 knees with bipolar lesions, five failed (12%): two of 30 patellofemoral bipolar lesions, two of six in the medial compartment, and one of six in the lateral compartment.
The large number of patients who had concurrent procedures performed to correct malalignment and maltracking illustrate the prevalence of these comorbidities in this patient population. As indicated in this and other studies, treatment success of ACI is dependent upon the careful detection and treatment of these comorbidities at the time of implantation; for example, we always perform unloading osteotomies in the setting of bipolar lesions. One concern of osteotomies is the potential to compromise the results of subsequent knee arthroplasty. Especially in young patients, the overall burden of surgery should be taken into consideration: it would not be useful to perform an osteotomy with cartilage repair, delaying knee arthroplasty by several years, if by doing so one would decrease the longevity and functional outcome of the arthroplasty, as suggested by early studies [2, 37]. More recently, however, multiple studies have demonstrated clinical outcomes of arthroplasty after tibial osteotomy that are not different from primary arthroplasty, even though the procedure is technically more challenging [31, 32, 40, 41, 58, 64]. The role of ACI in conjunction with realignment osteotomy has been viewed critically by many, who raise the valid question of how much additional benefit the cartilage transplant confers. If the majority of pain relief were derived from osteotomy, rather than ACI, one would expect revision rates of isolated osteotomy to be similar to those of osteotomy with ACI. However, isolated realignment osteotomy has demonstrated conversion rates to arthroplasty that approached 10% to 20% at 5 years and 20% to 50% at 10 years [8, 16, 61, 62], much higher than the reported rates for patients treated with ACI . We therefore believe that while the role of osteotomy is important to normalize joint biomechanics, ACI provides an important clinical benefit above and beyond that of the osteotomy.
At baseline, study patients had considerably lower physical functioning, greater bodily pain, and greater role limitations due to physical problems than a cohort of similarly aged people from the general U.S. population (Fig. 6). Assessments measured with the WOMAC pain, WOMAC function, modified Cincinnati knee rating system, KSS knee, and KSS function scales indicated that patients rated their baseline symptoms and function as poor to fair [6, 21, 36]. With limited treatment options, young osteoarthritic patients are a clinical challenge to treating surgeons. These patients have debilitating symptoms, a long active lifespan, and a strong desire to return to an age-appropriate level of function. We found that patients who were treated with autologous chondrocyte implantation for early osteoarthritis had clinically relevant reductions in pain at minimum of 2 years after treatment. On average, the percentage of patients experiencing severe and extreme pain and difficulty with various tasks including walking, bending and stairs fell by ¾. The findings from this study are consistent with the results reported previously in nonarthritic patient populations [42-44]. Furthermore, results from additional analyses showed that having a high tibial osteotomy or tibial tubercle osteotomy in combination with autologous chondrocyte implantation did not result in different outcomes when compared to treatment with autologous chondrocyte implantation alone.
Sixty-one percent of patients underwent repeat surgery, the majority for periosteum-related complications such as periosteal hypertrophy. This very high reoperation rate will decrease as collagen membranes replace periosteum for defect coverage; randomized trials in Europe have demonstrated reoperation rates of less than 5% with this technique . Importantly, all of these subsequent surgical procedures were arthroscopic, rather than open procedures, and none of the patients undergoing subsequent surgical procedures went on to requiring joint arthroplasty due to failure of ACI.
Our data demonstrate that autologous chondrocyte implantation results in clinically relevant reductions in pain and improvement in function, while apparently delaying the need for knee arthroplasty for over 5 years in 92% of patients. Careful and thorough discussion of the invasive surgical procedure, complex rehabilitation and long recovery, as well as high likelihood of repeat surgery, is paramount to ensure a reasonable level of patient expectations and satisfaction with the outcome. Given the limited treatment options for this subset of patients, ACI may be a plausible treatment for young osteoarthritic patients to delay the need for joint arthroplasty in the hope of obviating subsequent revision surgery, which is associated with much less satisfactory outcomes than primary procedures.
We thank Jae Hee Kang, ScD, Harvard School of Public Health, for her assistance with the statistical analyses.
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