The knee relies on ligaments for stability, including the Medial Patellofemoral Ligament (MPFL) and the Anterior Cruciate Ligament (ACL). The MPFL, on the inner side of the knee, connects the kneecap (patella) to the thigh bone (femur), preventing outward dislocation. The ACL, deep within the knee, connects the thigh bone and shin bone (tibia), preventing the tibia from sliding too far forward and controlling rotation. Injuries to either ligament can significantly impair mobility, often requiring surgery.
Understanding MPFL and ACL Injuries
The MPFL provides 50-80% of the resistance against lateral patellar displacement, especially in the initial 20-30 degrees of knee flexion. MPFL injuries typically occur during kneecap dislocations or partial dislocations, often from a direct blow, twisting, or abnormal knee anatomy. These incidents can stretch or tear the ligament, causing instability and recurrent dislocations. In contrast, ACL injuries often result from non-contact events like sudden stops, pivots, or changes in direction, common in sports such as basketball, soccer, and football. Direct blows can also cause an ACL tear, which can range from a mild stretch to a complete tear.
Surgical Approaches Compared
MPFL reconstruction replaces the damaged ligament with a new one, often from the patient’s own hamstring tendon (autograft) or a donor (allograft). The surgeon creates a new ligament pathway, often using small incisions and an arthroscope, anchoring the new ligament to the patella and femur to restore stability. ACL reconstruction also uses a graft to replace the torn ligament, as the ACL cannot typically be repaired by simply stitching it back together. Common autograft options include portions of the patellar, hamstring, or quadriceps tendons, with allografts from cadaveric donors also used. The surgeon drills tunnels in the tibia and femur to pass the graft through, securing it with screws or other fixation devices.
Recovery Timelines and Rehabilitation
Recovery from both MPFL and ACL reconstruction involves structured rehabilitation, though timelines and specific protocols differ. Following MPFL reconstruction, patients are typically off crutches within 1-2 weeks and can return to sedentary work. Physical therapy usually begins within the first week, focusing on reducing pain and swelling, restoring range of motion, and gradually strengthening the knee. Return to full sports participation after MPFL reconstruction typically ranges from 7 to 10.4 months.
ACL reconstruction generally involves a longer and more intensive recovery period. Patients typically begin walking with assistance and physical therapy immediately after surgery. The rehabilitation progresses through phases, initially focusing on regaining full knee extension and controlling swelling. Strengthening exercises and balance training begin early, with a gradual introduction of higher-impact activities like running between three and five months post-surgery. Full return to sports after ACL reconstruction typically takes 6 to 12 months, with many surgeons recommending waiting at least 9 months to allow for graft maturity and reduce re-injury risk.
Long-Term Outlook and Potential Complications
The long-term outlook for both MPFL and ACL reconstructions is generally favorable, with high success rates in restoring knee stability. For MPFL reconstruction, a significant percentage of patients successfully return to their pre-injury activity levels, with reported rates of return to sport exceeding 85%. The rate of recurrent instability events after MPFL reconstruction is relatively low, around 5.4%. However, some patients may not return to their prior level of activity due to persistent knee issues or apprehension about re-injury.
After ACL reconstruction, approximately 81% of individuals return to some form of sport, and about 65% return to their pre-injury level of participation. The risk of re-injury to the reconstructed ACL or the contralateral (opposite) ACL exists, particularly in younger, active individuals.
Potential complications for both surgeries can include persistent pain, stiffness, or nerve damage. The risk of developing osteoarthritis in the affected knee over time is a concern for both injuries, regardless of surgical intervention, due to the initial cartilage damage that can occur during the injury itself. Graft choice in ACL reconstruction can influence the re-tear risk, with autografts generally having a lower re-tear rate than allografts, especially in younger patients.