Abstract
INTRODUCTION
Clinical trials have generally failed to demonstrate superior clinical effectiveness of minimally invasive surgical approaches for total knee arthroplasty (TKA). The hypothesis of the current study was that avoiding incision of the quadriceps tendon would result in a significantly faster recovery of ambulatory function after total knee arthroplasty, compared to a technique that incised the quadriceps tendon.
METHODOLOGY
The MIKRO (Minimally Invasive Knee Replacement Outcomes) Study is a prospective, level 1 RCT that enrolled 128 patients with knee osteoarthritis who had failed non-operative treatment, and had decided to proceed with TKA. After skin incision, 64 patients each were randomized to either a subvastus (SV) or medial parapatellar arthrotomy (MPPA) approach. All surgeries were done with the same TKA implant, with anesthesia, post-operative analgesia, and physical therapy standardized for both groups. A Patient Diary methodology was used as the primary outcome measure for ambulatory function. During the first 8 weeks after TKA, a research assistant blinded to treatment assignment telephoned each patient and completed study forms that documented indoor and outdoor walking relative to use of ambulatory devices, as well as Knee Society Score (KSS) and the UCLA activity scale. The UCLA score and change in KSS from baseline at 4- and 12-week follow-up were used to begin the validation process for an Ambulatory Function Score (AFS) derived from diary indoor and outdoor scores.
RESULTS
There was a trend for the SV group to report more independent ambulation than the MPPA group at week 1 after surgery, as indicated by self-reported AFS (p < .052). Both treatment groups demonstrated significant week to week AFS gains through 5 weeks, after which weekly changes were minimal. As expected, outdoor AFSs were initially slower to improve than indoor AFSs, but by 6 weeks the initial 20-pt difference was less than 10-pts. AFS scores were significantly correlated with UCLA scores across all 8 weeks. Knee Society Scores (KSS) at baseline were rarely correlated with AFS scores across the 8 weeks. However, 1-month and 3-month KSS scores were significantly correlated with AFS scores at p < .05 beginning with weeks 2 or 3 and through week 8.
CONCLUSION
Avoiding incision of the quadriceps tendon during primary TKA resulted in a short-lived trend of quicker improvement in the AFS score in the SV TKA group versus the MPPA group. However, there appeared to be a similar rate of subsequent AFS improvement across the subsequent 8 weeks between the two groups. Preliminary results suggest a pattern of results – general improvement across 5–6 weeks that was maintained through the 8 weeks of evaluation, and significant correlations with UCLA and KSS scores after 2–3 weeks – that are consistent with the notion that the AFS is sensitive to change, and is variable depending on context (indoor vs. outdoor ambulation). Although related to UCLA and KSS scores, observed correlation magnitudes were not so high as to suggest that UCLA or KSS scores might be reasonable proxies for AFS.
