The purpose of this study was to investigate the self-reported clinical outcomes of patients with FTCL on 3T MRI who received Oxford UKA. All 101 knees treated with Oxford UKA showed FTCL on preoperative MRI, while 89 showed bone-on-bone lesions on X-ray, 80 showed BME on MRI, and 81 showed MMRT on MRI. We thus assessed the efficacy of MRI as an alternative screening tool based on the outcomes of these patients. All patients, including those without radiographical evidence of bone-on-bone lesions, were satisfied following the Oxford UKA. Our results thus indicate that FTCL on 3T MRI, and not bone-on-bone lesions on X-ray, could be a possible indication for Oxford UKA.
The radiological decision aid was proposed in 2016, which used the weight-bearing anteroposterior, varus stress, and Rosenberg views to evaluate the medial compartment [9]. Despite this tool involving extensive radiographical investigation of the medial compartment, further studies revealed that it has a low overall sensitivity (70.1%) and specificity (76.2%), which could be a result of the overall high false-negative rate (22.7%) [10]. Therefore, many studies have sought a way to identify patients who do better following Oxford UKA even without bone-on-bone lesions. Niinimäki et al. [20] reported higher reoperation rates for patients selected using a preoperative medial to lateral joint space ratio of > 40% or > 2 mm of preoperative medial joint space. Maier et al. [21] also reported comparable outcomes for patients without bone-on-bone lesions, supporting the recommendation of MRI as a preoperative evaluation tool for predicting clinical outcomes.
Hamilton et al. [13] reviewed 36 Oxford UKAs and reported that FTCL or subchondral edema on preoperative MRI did not significantly affect the functional outcome in patients with PTCL at the time of operation. Jacobs et al. [22] reviewed 28 Oxford UKAs and reported that tibial BME lesions were related to worse pain scores and lower satisfaction (73% vs. 100%; P = 0.03), which may be attributed to a combination of BME and other technical factors. In contrast, Jacobs et al. [15] later graded bone marrow lesions (BMLs) using the MRI Osteoarthritis Knee Score criteria following 174 Oxford UKAs, and demonstrated that lesions in the tibia and medial compartments were correlated with better postoperative functional scores. They also reported that more severe BMLs were related to higher knee society scores [15]. Berend et al. [14] reviewed 152 Oxford UKAs and categorized them into four groups according to presence or absence of medial tibial BMLs and FTCL. They reported that neither medial tibial BMLs nor PTCL were associated with inferior outcomes or higher revision rates [14]. Our study found that there were similar patient-reported outcomes even for patients without BME lesions. Another study described small chondral lesions, such as cracks or fissures, that could result in a low signal intensity due to the lower proteoglycan and water content, which may be filled with high-signal-intensity fluid [23]. These lesions could be associated with reactive BME if deeply extended, which may explain the high proportion of patients with BME lesions in our study.
Recent studies have shown that MMRT is related to increased peak contact pressure, secondary osteoarthritis, and spontaneous osteonecrosis of the knee [24, 25]. Tagliero et al. [16] showed that Oxford UKA provided patients who had arthritis secondary to MMRT with comparable outcomes to those who had primary osteoarthritis. Our results similarly show that patients with MMRT do well after surgery. We believe that whatever the cause of FTCL, patients can do well after surgery.
Many advancements have been made in MRI technology and protocols in the past decade. Several previous studies have reported that the diagnostic accuracy of MRI is low, especially for low-grade chondral lesions. However, high sensitivity (81%) and specificity (99%) for grade IV lesions with exposure of the subchondral bone has also been reported. [26]. Another recent study compared the location and severity of chondral lesions and revealed that MRI evaluation, although generally underestimated, was more precise for the medial compartment [27]. Therefore, we believe that FTCL on MRI could be useful for screening patients for Oxford UKA treatment. However, the low sensitivity of MRI may falsely diagnose patients with FTCL as having only PTCL. Because of its technical advantages, 3T MRI is becoming widespread in clinical practice. 3T MRI systems have a higher signal-to-noise ratio and spatial resolution and a thinner section thickness than 1.5T systems [17]. A study involving 200 patients compared 3T MRI with 1.5T for each patient and demonstrated the higher sensitivity of 3T MRI (sensitivity: 69% vs. 60%) [18]. It also confirmed that 3T MRI has a higher accuracy (sensitivity: 94.4%, specificity: 98.5%) for grade III chondral lesions (full-thickness cartilage defects) than for lower-grade chondral lesions [18]. Recently, a meta-analysis reported overall higher sensitivity and specificity for 3T MRI than for 1.5T [19]. They also found that the AUC was greater for 3T MRI (0.9106, vs. 0.7867 for 1.5T; P < 0.05) and concluded that 3T MRI was more effective for diagnosis [19]. Since our study used a 3T MRI system, the high-grade chondral lesions and FTCL we observed were specific findings that could indicate potential candidates for Oxford UKA treatment.
This study was not without limitations. First, we conducted a retrospective analysis of prospective data. Selection bias may have existed during the physical examinations and patient-selection process, which were conducted by a single surgeon. Second, since we only analyzed Oxford UKA patients with FTCL, there was no control group with PTCL in the study. We therefore could not tell if there were potential candidates for Oxford UKA with PTCL. Further studies are required to properly identify patients with PTCL who would benefit from Oxford UKA. Third, due to the short-term follow-up period of six months postsurgery, we were unable to investigate associations between reoperation and the absence of bone-on-bone lesions. Previous studies have indicated that the most common reason for reoperation is unexplained pain. There were no complaints of pain during the six months of our study. We will, however, keep following-up with our patients and will record reoperation rates.