Reoperative characteristics after microfracture of knee cartilage lesions in 454 patients

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1 DOI /s y KNEE Reoperative characteristics after microfracture of knee cartilage lesions in 454 patients G. M. Salzmann B. Sah N. P. Südkamp P. Niemeyer Received: 4 August 2011 / Accepted: 15 March 2012 Ó Springer-Verlag 2012 Abstract Purpose There is only limited information on those patients who fail following microfracture treatment at the knee joint. Evaluation was made of factors associated with treatment failure and clinical outcome assessment among this collective. Methods The study included a total of 560 patients who had previously undergone microfracture for the treatment of symptomatic knee joint cartilage lesions. For the remainder of this study, inclusion criteria were patients that underwent reoperation at the initially operated knee joint (index knee) due to symptoms related to the primary site of microfracture intervention (failure patients) with a minimum postoperative follow-up of 2 years. The remaining cohort of patients served as internal control (non-failure patients). Chart reviews were performed to identify patient and defect characteristics. Patients were evaluated for postoperative Lysholm knee scores, Tegner activity scale, as well as preoperative and postoperative numeric analogue scales (NAS) for function and pain (10 = highest possible function, no pain). Results A total of 454/560 (81.1 %) subjects were completely evaluated. Overall, /454 patients (26.9 %) (age at operation 43.9 ± 14.1 years, 56 female, BMI 25.8 ± 3.6, 30 smokers, 61.1 ± 68.3 month symptom duration, postoperative follow-up 5.0 ± 2.1) met the inclusion criteria. The postoperative Lysholm score was 63.0 ± 24.6 and the Tegner score was 4.0; NAS function improved G. M. Salzmann (&) B. Sah N. P. Südkamp P. Niemeyer Department of Orthopaedic and Trauma Surgery, University Medical Center, Albert-Ludwigs University Freiburg, Hugstetter Strasse 55, Freiburg, Germany giansalzmann@yahoo.com from 2.8 ± 1.8 to 4.8 ± 2.2 (P \ 0.001), and NAS pain improved from 3.2 ± 2.1 to 5.0 ± 2.4 (P \ 0.001). Exclusively, the overall defect size/knee joint was smaller (P = 0.006), postoperative follow-up was longer (P = 0.002), and existense of previous surgery (77.2 vs %, P \ 0.001) was more frequent in failure subjects when comparing to non-failure patients (n = 331). The overall clinical outcome among failure subjects was significantly worse when comparing to non-failure subjects. Regression analysis identified that lower preoperative NAS values, being a smoker, and patello-femoral lesions were associated with a higher probability of reoperation. Conclusion Within the collective presented here, microfracturing was associated with a high frequency of reoperation. Clinical outcome is worse when compared with that of patients without reoperation. Specific parameters can be identified that increase the eventuality of failure following microfracture treatment. Level of evidence IV. Keywords Microfracture Cartilage Outcome Failure Complication Chondrocyte Introduction The treatment of microfracture [28] has evolved and remains a standard first-line operative technique for treatment of small-diameter (2 3 cm 2 ) articular cartilage lesions without significant underlying osseous deficiency [7]. The clinical outcome has been and is often used for comparison with that of autologous chondrocyte implantation (ACI). Relating to current evidence there is a clear trend for an improved outcome following ACI, in particular for lesions with increasing dimensions [1, 8 10, 22, 23].

2 Treatment algorhithms [5] enlist microfracture as a first line option for therapy of small-diameter lesions with osteochondral grafting as an alternative [3]. It remains imperative that one focuses on patient-specific and defectspecific variables, which should guide tailored treatment options for every individual. This aspect becomes particularly important against the background of certain complications that may arise following the course of microfracturing at the knee joint, which can nowadays be detected early using quantitative imaging [20]. According to a current meta-analysis presented by Mithoefer and colleagues, there are several parameters having the potential to strongly impair the clinical outcome, which ultimately may result in a failure [15]. While intra- and perioperative complications remain a mere curiosity, clinical failure during the postoperative course has been previously described with considerable frequency, being variable as well as time dependent. The failure/revision rate has been reported to be approximately 2.5 % at less than 24 months postoperatively, increasing to 2 31 % when surgery lasted 24 months and longer [15]. However, these data were filtered out of studies with a different scope [4, 6, 8, 9, 13, 14, 17, 25, 26]. No previous study has concentrated on failure patients as the primary focus. For the remainder of this study we focused on reoperation at the initially operated knee joint (index knee) due to symptoms related to the primary site of microfracture intervention as a failure. We hypothesize that there are specific patient and/or defect characteristics that are associated with an increased failure rate. The aim of this study was to identify variables associated with failure during the postoperative course and to report on the clinical outcome among this collective of patients. Materials and methods Between January 2001 and December 2008, a total of 560 patients were treated at our institution for symptomatic knee cartilage lesions using the microfracturing technique. We conducted a retrospective chart review and attempted a telephone interview with every patient during the time span 2009 through The interviews were done by an independent investigator not involved in patient care at our institution. All study data were anonymized during the study process. For the purpose of this report we isolated patients that underwent reoperation/revision surgery at the index knee joint with pain related to the initial operative site that had been previously treated using the microfracture technique with a minimum postoperative follow-up of 2 years. Subjects that underwent reoperation are described as failure, while the remaining patients are described as non-failure. Patients who had suffered any trauma leading to reoperation at the index knee followig the initial microfracture were excluded. The study was approved by the local institutional review board (Ethik-Kommission der Albert-Ludwigs-Universität Freiburg, ethical approval no. 36/11), and all patients gave oral consent to the interview. Surgery The surgical approach has been described before [28]. Patients with a clinically clear symptomatology, adequate cartilage lesion(s) on preoperative magnectic resonance imaging (MRI), no advanced pathologic meniscal condition, absence of varus/valgus deformity exceeding the tibiofemoral malalignment by over 5, limited active knee flexion below 120 or an extension deficiency exceeding 20, significant patellofemoral malalignment, high-grade ligamentous instability, active local or systemic infections, or inflammatory arthropathy or advanced knee osteoarthritis (OA) are generally considered for surgery. Patients furthermore were expected to be compliant with fulfillment of the extended and standardized rehabilitation program [11]. The final decision to proceed with microfracturing was made during knee arthroscopy depending on the lesion characteristics and general intraarticular knee morphology (very infrequently a decision was made against the initial intent of microfracture during arthroscopy). The indication was given for full-thickness chondral defects (in selected cases also in grade II and IV lesions), grade III B or C according to the International Cartilage Repair Society (ICRS) classification system [31]. Kissing lesions, uncontained lesions, large-diameter lesions ([3 4 cm 2, exceptions apply), more than 2 3 lesions/knee, osteochondral defects, and knee OA are contraindications for microfracturing (at our institution). Rehabilitation was 6 weeks of partial weight-bearing for all lesions treated. Patients were advised to achieve full weight-bearing at 8 9 weeks post surgery with free range of motion at all times for tibiofemoral defects. Range of motion using a knee orthosis (2 weeks 30 flexion limit, followed by another 2 weeks 60 flexion limit with another final 2 weeks 90 flexion limit) was limited at the patellofemoral joint to minimize excessive strains at this particular compartment. Continous passive motion was intended during the first 6 weeks after the operation in every patient. Return to sports was allowed at 6 9 months postoperatively depending on patient and defect characteristics as well as individual physical shape. Outcome measures Chart reviews were performed to identify patient characteristics: age, gender, BMI, symptom duration until surgery, timely interval from surgery to interview (follow-up time), previous surgery, smoking habits; and defect

3 morphology: location, diameter in square centimeter, depth according to ICRS. Telephone interviews were done (following appropriate behavior according to day and time) to record for the postoperative clinical outcome: subjective International Knee Documentation Committee (IKDC) Knee form score [2], Lysholm score [12], Tegner activity scale [30] as well as for a preoperative (patients were retrospectively asked how they felt before the operation) and postoperative numeric analogue scale (NAS) for pain (NAS-P) and function (NAS-F) with 10 representing no pain and 0 representing maximal imaginable pain. Furthermore, patients were asked about general subjective postoperative symptoms (improved, constant, deterioration), about satisfaction with surgery (very satisfied, satisfied, partially satisfied, not satisfied) and whether patients had another surgery at the index knee (= the knee joint that had initially been treated with microfracture) without re-trauma and symptoms related to the original operative site. For clinical outcome among patients that underwent reoperation, the outcome is given at the time point before the reoperation in order to mirror the final result of the microfracturing procedure. The first cartilage lesion among knee joints was the largest among all lesions/knee joints when dimension (not depth) was concerned. The second lesion was the second largest, etc. Statistical analysis Statistical analysis was performed using the software package SPSS version 17 (SPSS Inc., Chicago, IL, USA). All data were tested for normal distribution using the Kolmogorov-Smirnov test. Afterwards, data were compared using t tests or Mann-Whitney U and Wilcoxon signed rank tests. Group data were compared using oneway analysis of variance or Kruskal-Wallis analysis. Correlations were performed using Spearman s correlation coefficient (r). Following the chi-square test to define independence, linear regression analysis was done to analyze the effects of patient and/or defect characteristics as well as preoperative NAS values on the final clinical outcome. Unless otherwise stated, descriptive results are demonstrated as the mean ± standard deviation (SD). The significance level was defined at P \ 0.05 for all tests. Results Study cohort A total of 454/560 (81.1 %) consecutive patients were succesfully contacted via telephone. Of these subjects, /454 (27.1 %) met the outcome criteria and underwent reoperation (failure) at the index knee due to symptoms related to the initial microfracturing site. The timely interval between initial microfracturing and reoperation was 1.6 ± 1.8 years. Three hundred thirty-one (72.9 %) patients did not undergo reoperation (non-failure) at the index knee joint at the time of the interview. Among failure subjects, a total of 78 (63.4 %) patients reported a knee trauma causing symptoms leading to the initial microfracture procedure, while a total of 206 (62.2 %) of the non-failure subjects reported previous trauma, demonstrating no statistical difference for this particular parameter. Patient characteristics When comparing patient characteristics of failure with non-failure subjects, failure subjects had significantly more previous surgeries to the index knee (1.9 ± 2.1 versus 1.2 ± 2.1, P \ 0.001), a higher rate of general existence of previous surgery at the index knee (77.2 vs %, P \ 0.001), and a longer timely interval from the initial microfracture operation until the interview (5.0 ± 2.1 vs. 4.4 ± 1.9 years, P = 0.002) (Tables 1, 2, 3). The remaining patient characteristics were not significantly different. Table 1 With the exceptions previous surgery and follow-up time, patient characteristics were similar among failure and non-failure subjects Failure subjects Non-failure subjects P value Total number of patients 331 n/a Age at surgery, years 44.2 ± ± 13.7 n.s. Age at examination, years 49.2 ± ± 13.6 n.s. Male/female, total 67/56 194/137 n.s. BMI, kg/m ± ± 4.3 n.s. Symptom duration, months 61.3 ± ± 97.9 n.s. Previous surgery 1.9 ± ± 2.1 \0.001 Smoking/non-smoking, total 30/93 68/263 n.s. Follow-up, years 5.0 ± ±

4 Table 2 The item defect stands for number of cartilage lesions/knee joint Failure subjects Non-failure subjects Number of defects 1.2 ± ± 0.5; (P = 0.245) Defect size/knee, cm ± ± 1.6; (P \ 0.001) Defect 1 (n = ) 2 (n = 22) 3 (n = 2) l (n = 250) 2 (n = 67) 3 (n = 14) Defect size/defect, cm ± ± ± ± ± ± 0.8 ICRS ICRS 3B ICRS 3C ICRS Medial/lateral condyle 61/9 5/2 171/31 19/12 0/1 Patella/trochlea 8/26 4/2 1/0 31/68 5/22 1/4 Medial/lateral tibia 13/6 6/3 1/0 16/14 14/10 3/5 The largest defect according to diameter is encoded as defect number 1, the second largest number 2, and the third largest defect number 3. There were n = knee joints with only one lesion, a total of n = 22 added to those by having a second lesion, while another n = 2 were added with a third lesion Table 3 All postoperative clinical scores were significantly different between failure and non-failure patient populations Failure Non-failure P value Postoperative IKDC, percent 58.8 ± ± 19.1 \0.001 Postoperative Lysholm 62.8 ± ± 19.8 \0.001 Postoperative Tegner 3.3 ± ± 1.7 \0.001 Preoperative NAS-P 3.1 ± ± 2.0 n.s Postoperative NAS-P 5.2 ± ± 2.4 \0.001 Preoperative NAS-F 2.8 ± ± 1.7 n.s Postoperative NAS-F 4.8 ± ± 2.2 \0.001 Improvement, % of cases 13.8/45.8/ /45.4/15.6 n.s Satisfaction, % of cases 22.0/27.6/13.8/ /36.6/11.1/11.0 \0.001 Postoperative improvement when comparing to preoperative was categorized in percent of patients as better/constant/worse. Satisfaction with the clinical outcome of the procedure was categorized in percent of patients as very satisfied/satisfied/partially satisfied/not satisfied. The P value for the parameters Improvement and Satisfaction after quantification into nominal parameters and thus comparing overall means. The Tegner value is given as median Defect characteristics When comparing defect characteristics of failure with nonfailure patients, failure subjects had significantly smaller total defect dimensions/knee (2.1 ± 1.7 vs. 3.3 ± 1.6 cm 2, P \ 0.001) as well as significantly smaller dimensions of the first lesion (2.0 ± 1.6 vs. 2.6 ± 1.8 cm 2, P = 0.006). Remaining defect characteristics were not significantly different. Regression analysis When measuring regression analysis (dependent variable IKDC) for all patients (n = 454), the independent variables absence of previous knee trauma (P = 0.027), longer symptom duration (P = 0.004), female gender (P = 0.006) as well as existense of previous surgery to the index knee (P = 0.009) were related to a depressed clinical outcome. Interestingly, the general fact of smoking versus nonsmoking did not affect the outcome, while among smokers, subjects who smoked less had significantly better outcomes. When measuring the same regression analysis for failure subjects (n = ), the variables absence of previous knee trauma (P = 0.027), longer symptom duration (P = 0.038), lower preoperative NAS pain (P = 0.05) and function (P = 0.05), smoking (P = 0.03), and follow-up time (P = 0.05) were related to a depressed clinical outcome. Cigarette quantity had no further effects. When measuring the same regression analysis for non-failure subjects (n = 331), the variables longer duration of symptoms (P = 0.006), female gender (P = 0.019), and existence of previous surgery (P \ 0.001) were related to a decreased clinical outcome. This information remained similar when calculating regression using the remaining clinical outcome parameters as the dependent variable.

5 When calculating regression analysis (of all 454 subjects) including all patient and defect characteristics with the dependent variable reoperation, both preoperative numeric analogue scales (function, P = 0.008; pain, P \ 0.001), smoking (P = 0.01) and location of the largest (and therefore first) lesion (P = 0.016) had a significant impact. Lower preoperative NAS values, smoking, and patello-femoral lesions were associated with a higher probability of reoperation. The quantity of cigarettes did not result in a different outcome among failure subjects. Discussion The most important finding of this study was the fact that microfracturing at the knee joint leads to reoperation at the index knee in approximately one-fourth of cases, commencing on average 18 months after the initial operation. Patients that underwent reoperation suffered from smaller cartilage lesions and had a higher quantity of previous surgeries in comparison to the entire collective of consecutive patients. Factors that are significantly connected to an increased likelihood of reoperation are a preoperative subjective sensation of less function and more pain, smoking, and defects located at the patello-femoral compartment. General intra-, peri-, or post-operative complications during the course of arthroscopic knee joint microfracturing are very rare. These compare well with complications that appear during every other knee arthroscopy and are therefore not specific [21, 24]. Steadman and colleagues in 1997 described no surgery-related complications in 1,275 microfracture patients [29]. However, problems arise during the extended postoperative course of this procedure. Several authors have previously touched upon this particular topic. However, none of these has specifically concentrated on that matter [26]. When comparing single versus multiple lesions among all patients (n = 454) as well as non-failure patients (n = 331) from our collective, subjects with single lesions had significantly better clinical outcomes. This was not true for failure patients where there was no difference between patients with one compared to multiple lesions (data not shown). Mithoefer and colleagues previously reported on the prospective outcome among 48 subjects after a knee joint microfracturing procedure. The authors did not specifically report on failure patients [16]; however, 25 % were rated as fair, and 8 % of patients were rated as poor at the time of the latest followup. These numbers reflect the proportion of failure subjects among our cohort (27.1 %) as well as subjects that were either partially satisfied or not satisfied with the procedure (28 % of all n = 454 subjects). Among the parameters that were described by Mithoefer to be associcated with lower clinical scores (older patients, higher BMI, longer symptom duration, less defect fill on MRI), solely the variable symptom duration compares to our information. This parameter, however, did not significantly increase failure probability during regression analysis of all patients analyzed for this study. Patients from our cohort underwent reoperation at an average 1.6 years (= 18 months) after the initial microfracture related to symptoms at the initial microfracturing site. This outome is in line with information from Kreuz and coworkers [11], who reported on symptom deterioration beginning 18 months after surgery. This phenomenon was significantly pronounced in patients aged older than 40 years, while also patients with patello-femoral lesions were negatively affected. While generally age demonstrated an impact on the clincial outcome following microfracturing, this parameter was of lesser influence among our patients who were considerably older. This may be because of the specific properties in which older chondrocytes or mesenchymal stem cells have less mitotic activity or responsiveness to physicobiochemical stimuli, and there may have been lesser effects. Solheim and co-authors [25] recently reported on the clinical ouctome in a total of 110 patients (median age 38 years, median follow-up 5 years) following microfracturing at the knee joint. The median symptom duration (40 months) was similar to that in our cohort of patients (median of 36 months in all n = 454 subjects) defining the two populations as comparable, bearing in mind that preoperative symptom duration has major effects on the final outcome. In that study the authors registered 24 failures (22 %) overall. This number compares very well with the findings of our study. A failure was defined (as within our study) as a new surgical procedure (during the follow-up period and in the same knee) with the intention to treat the initial cartilage lesion. Fourteen out of 76 cases (18 %) in the failure group had a single defect, and 10 out of 34 cases (29 %) in the group had 2 or 3 lesions. Failure rates following microfracture treatment between 20 and 30 % were also reported by Knutsen (23 %) in 2004 [9] and by Steadman [27] in an advanced age patient population. At 5-year follow-up in the same collective of patients, Knutsen reported 23 % failures following the microfracturing procedure [8]. Compared to the findings at 2-year follow-up, the failure rate had strongly increased, which retrospectively underlines younger published data. The failures occurred at a mean of 26.2 months after the autologous chondrocyte implantation and 37.8 months after the microfracture treatment (n.s.). Interestingly, the same failure percentage was reported among ACI patients. This number however was not affirmed by other ACI trials, and one has to note that ACI has to be considered a much more complex procedure [18, 19, 32].

6 When respectively analyzing (calculating with patient and defect characteristics) each collective all patients, failure patients, and non-failure patients we discovered that exclusively the parameter symptom duration significantly affected the clinical outcome among all patients, among failure patients as well as among non-failure patients. Regression analysis outcome was very similar among all patients as well as non-failure patients (longer symptom duration, female gender, previous surgery depressed the clinical outcome) with the exception of the parameter absence of previous trauma. This parameter, however, had a significant impact on failure subjects. The parameters smoking and preoperative numeric analogue scale values were solely significant among failure subjects and during regression analysis among all patients with the factor reoperation as dependent variable. Eventually, the variable defect location was the only parameter to appear to have a significant impact (considering all regression results) when measuring for reoperation rate among failure subjects. Finally, Mithoefer and colleagues [15], in a systematic analysis, reported that failure after microfracture is generally variable and time- dependent. The authors discovered that the early revision rate generally was 2.5 % at 2 years and increased to % between 2 and 5 years postoperatively. This basic information compares very well to data presented by Knutsen at 5-year follow-up [8]. Revisions as failures were reported at a mean of 8 38 months after microfracture. Better results were generally found without previous surgery, with younger age, shorter symptoms, lighter patients, higher preoperative activity, and good defect fill. Data from our study also display that the event of failure following microfracture treatment is variable and time dependent. Symptom deterioration generally commences at 18 months potoperatively, which can be considered a decisive point after microfracture surgery. Among the patient and defect variables we analyzed/were able to analyze in our study to identify factors that increase reoperation probability, exclusively the parameter preoperative activity (as reflected by NAS scores) can be compared to the variables defined by Mithoefer. Nevertheless, among all patients from our study, also absence of previous surgery and shorter symptom duration were clearly associated with an improved clinical outcome. This assertion, however, cannot be applied for failure candidates. Clear limitations of this study are to be found in its retrospective nature. Patient age was advanced compared to the populations in other studies reporting on the clinical outcome following microfraturing. Postoperative MRI following microfracturing is not considered routine at our institution. Postoperative MRI is only available for selected cases, and it was missing for the majority of patients. Expoloring defect filling and possible regeneration characterization were not possible. Strengths of this study are that our collective of patients can be considered quiet large compared to the existing studies. Furthermore, postoperative follow-up circumscribes a time point that can be described as definitive following microfracturing. Conclusion In conclusion, this study revealed that among this collective of consecutive patients, failure, defined as reoperation at the index knee, appears in approximately one-fourth of patients. Certain patient- as well defect-associated parameters can be identified to escalate the likelihood for reoperation. The same information is true for all patients analyzed during this study. 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