The Kim study shows, again, that we must have clear indications for TTO in the setting of patella instability. We know from Liu and Shubin Stein that isolated MPFL reconstruction works well for recurrent patella instability. What we do know however, in addition, is that some recurrent instability patients will develop severe lateral patellofemoral arthritis if we do not balance tracking at the time of stabilization. TTO prevents this lateral joint breakdown when a patient has established lateral tracking. While most patella instability patients do not need TTO, some do, and we have to get better at determining who those patients are.

I was interested to read the article by Jong-Min Kim, MD, and colleagues reporting the clinical outcomes of MPFL reconstruction with or without TTO for patellar instability. The treatment of patellar instability and malalignment remains a challenging topic with many unanswered questions. Perhaps the largest challenge facing surgeons today is identifying the best surgery to address multiple variables: ligamentous disruption or laxity, tibial tubercle offset, coronal and rotational alignment, trochlear morphology, patellar height, soft tissue balance and patient-specific kinematics. How do we determine a surgical plan and where do we set our limits?

The current study is perhaps the best scientific effort to date comparing MPFL reconstruction in isolation (iMPFL) or in combination with tibial tubercle anteromedialization osteotomy (MPFL-TTO). Kim and colleagues retrospectively evaluated outcomes in a cohort of 81 patients with a tibial tubercle-trochlear groove distance (TT-TG) between 15 mm and 25 mm. To my knowledge, this study is the only direct comparison of these surgical options in which the cohorts demonstrated similar mean preoperative TT-TG, hip-knee angle and trochlear dysplasia profiles.

The results showed equivalent functional outcomes and complications between iMPFL and MPFL-TTO groups, with a 6.7% overall failure rate (iMPFL n=2/36; MPFL-TTO n=3/45). The most notable finding of the study may have been that outcomes were equivalent even after stratification into groups with TT-TG greater than and less than 20 mm. The authors concluded that iMPFL is a safe and reliable treatment for patients with TT-TG between 15 mm and 25 mm, “without the disadvantages derived from TTO.” 

The current study adds a unique dataset to the literature by comparing iMPFL and MPFL-TTO in cohorts with similar preoperative malalignment parameters. Two previously published articles comparing iMPFL and MPFL-TTO have also demonstrated similar outcomes and complication rates between these surgical options in cohorts of 129 and 95 knees, respectively (Mulliez and colleagues and Sherman and colleagues). However, each of these series assigned MPFL-TTO treatment selectively based on the presence of increased malalignment, patella alta or trochlear dysplasia (Mulliez and colleagues) or based on surgeon preference (Sherman and colleagues). As a result, the combined surgical group demonstrated more significant preoperative malalignment in both series. Both studies demonstrated similar functional outcomes, failure rates and complications between surgical groups. Due to the inequities across surgical groups, neither study helped to define an upper limit for iMPFL in the setting of malalignment. I believe the current study provides stronger short-term evidence to support iMPFL as an acceptable option to correct instability even in the setting of TT-TG of greater than 20 mm. 

However, while the authors deserve a great deal of credit for this research, I feel we must exercise caution before accepting the manuscript as an indictment of bony realignment. The authors restate in their conclusion the misconception that there are major “disadvantages derived from TTO.” This stands in direct conflict with their own evidence. The study clearly showed that overall complication and failure rates were not significantly worse when adding an osteotomy. These objective findings reinforce the outcomes of the two prior published cohorts. While the differences in early recovery and rehabilitation are likely to affect shared decision-making, the equivalent complication rates should serve to dispel apprehension regarding TTO morbidity among surgeons and patients alike. While short-term surgical success rates were good for both procedures, the study also clearly demonstrates the negative impact of malalignment on failure rates. Four of the five patients with recurrent instability in this study had a preoperative TT-TG of greater than 20 mm (postoperative TT-TG for the TTO subset is not reported). Arguably, the equivalent failure rates of iMPFL and MPFL-TTO may not represent the success of iMPFL. It may simply represent equivalent failure. Overall, these findings suggest that a more complete solution is needed in the setting of more severe malalignment.

Why then, despite the presence of a vague consensus, do we struggle to effectively define the population most likely to benefit from TTO? Why did the addition of TTO in the current study fail to decrease recurrence relative to iMPFL? Perhaps it is because we continue to oversimplify a complex problem. We have largely failed in attempts to simplify surgical indications for a 3D problem to cutoff values in single plane measurements (eg, Q-angle, TT-TG, TT-PCL). Is it surprising that the generalized application of an osteotomy that only corrects select variables fails to outperform iMPFL? The current study highlights our inability to personalize surgical indications and procedures in this diverse population, with the result that early outcomes are generally equivalent. Luckily, help may be on the way. New technologies such as 3D modelling, templating and printing are emerging within the patellofemoral community. These tools hold promise for a deeper understanding of patellofemoral joint kinematics, a more targeted use of TTO and/or other osteotomies, and a meaningful reduction in our failure rates.

Even if recurrence rates for iMPFL and osteotomies remain equivalent in the future, there are additional arguments in favor of bony realignment. While the current study suggests that adding TTO to MPFL may not improve functional outcomes or improve stability in the short term (mean 25.2 months), malalignment creates long-term morbidity that iMPFL cannot address. Cadaveric models simulating an elevated TT-TG have shown that iMPFL reconstruction cannot correct patellar tilt, patellar lateralization or peak contact pressures with tubercle lateralization beyond 5 mm (Stephen and colleagues). Even in the absence of recurrent instability, similar altered mechanics lead to chondral degeneration in patients presenting to our clinics. Coronal and rotational deformity in patellar instability patients may have similar consequences, with implications for degeneration in the lateral knee and hip, respectively (Parker and colleagues). While iMPFL may solve instability in the short term, only osteotomy offers the potential to improve limb kinematics and preserve cartilage in the setting of deformity.

In conclusion, the study by Kim and colleagues fits well with a common illustration from my orthopedic training: “A patient with patellar malalignment and instability is like a horse-drawn wagon with a bent axle. Hitching on a new horse and pulling harder on the reins may make it go straight for a little while … ”  The iMPFL may be a strong horse, and it may get us farther than we hoped, but where does the road end?  We must continue to identify better ways to fix the wagon.

References:

Mulliez A, et al. Knee Surg Sports Traumatol Arthrosc. 2017;doi:10.1007/s00167-015-3654-0.

Sherman SL, et al. Orthopaedic Journal of Sports Medicine. 2019;doi:10.1177/2325967119S00307.

Stephen JM, et al. Am J Sports Med. 2015;doi:10.1177/0363546515597906.

Parker EA, et al. Arth Sports Med Rehab. 2021;doi:10.1016/j.asmr.2021.07.029.