Biomechanical studies have shown increased medial patellofemoral force and pressure with a malpositioned femoral tunnel. Clinical reports describe knee pain, medial patella overload, medial patella subluxation and knee stiffness in select cases with femoral tunnel malposition. However, larger clinical studies have not shown any correlation with tunnel position and clinical outcome at short-term follow-up.
Servien and colleagues had 10 of 29 femoral tunnels malpositioned on MRI but no difference in outcomes when comparing groups. McCarthy and colleagues evaluated postoperative radiographs in 60 patients and found 65% of femoral tunnels were malpositioned. However, there was no difference in clinical outcomes.
There are several possibilities to explain these findings. First, current outcome instruments may not be sensitive enough to identify differences between groups. Servien and colleagues only reported subjective IKDC outcomes and McCarthy and colleagues only reported KOOS scores. Second, short-term follow-up may not be long enough to show the effects (patellofemoral degenerative changes) of malpositioned tunnels. Third and most importantly, femoral tunnel position is only one part of the procedure. The ability to set the correct graft tension/length during medial patellofemoral ligament (MPFL) reconstruction likely plays a larger role in determining outcomes. The MPFL is a checkrein ligament designed to guide the patella into the trochlear groove during the first 30° of knee flexion. Beck and colleagues showed that 2 N of graft tension restored normal patella translation. Higher loads (40 N) limited motion and increased medial patellofemoral pressure.
Femoral tunnel position
Clearly, femoral tunnel malposition does not always lead to a poor outcome. I have seen many patients who have had a MPFL reconstruction at an outside institution with an anterior and proximally positioned femoral tunnel and excellent clinical outcome. However, anatomic femoral tunnel position plays a role in maximizing outcomes and providing the best chance of excellent short-term and long-term success.
There are many resources to determine appropriate femoral tunnel position intra-operatively, with use of fluoroscopic and anatomic landmarks. Similar to the evolution of ACL reconstruction surgery, anatomic MPFL graft positioning should not be sacrificed no matter what technique or fixation method is used.
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- Matthew Bollier, MD, is from the Department of Orthopaedic Surgery, University of Iowa Sports Medicine Center.
- Disclosure: Bollier has no relevant financial disclosures.