“Pin the Tail on the MPFL” Identification by Palpation - Results

OBJECTIVES: Medial patellofemoral ligament (MPFL) reconstruction has become increasingly popular to treat patellar dislocation. Studies have noted the importance of recovering the anatomic insertion of the MPFL and that reconstruction should be performed within 5mm of the native insertion site to avoid biomechanical complications. Currently radiographic imaging is used to locate the MPFL insertion site at Schottle’s point. This study investigated the viability of utilizing palpation to locate the MPFL insertion site for proper MPFL reconstruction. METHODS: Thirty-eight patellofemoral specialists attending IPSG were selected to participate in this study with a mean of 15.9 years in practice (median 14, range 1-39). Using a single fresh-frozen human cadaveric knee, each specialist individually performed surface palpation of the anatomical landmarks and inserted a dissection pin at the purposed MPFL femoral insertion site. Radiographic images were taken of each pin placement. At conclusion, the cadaveric leg was dissected and forceps were placed at the distal and proximal end of the MPFL insertion with a dissection pin in the middle of the insertion and a radiographic image was taken of this. Images were analyzed using ImageJ software to determine the distance and angle from the MPFL insertion center to the specialist’s pin location. RESULTS: Length and angle measurements were taken three times and averaged for each sample. The bridge of a forceps was utilized as a scale for the images (2.325 pixels/mm). Average distance was found to be 3.18 ± 2.55 mm with an average angle of 161.2 ± 74.4° relative to the anterior direction indicating 0°. Seven of thirty-eight (18%) samples were more than 5mm from the native insertion site. CONCLUSION: With an average pin displacement of 3.18mm, it was seen that most specialists could accurately determine MPFL insertion location accurately without the use of radiographic equipment. On average, the displacement angle of 161.2° indicates the pin was typically located more posterior than the MPFL insertion site. Seven measurements exceeded 5mm distance from the MPFL insertion, which would be concerning for biomechanical effects on the patellofemoral joint if the repair was placed at the pin location. CLINICAL RELEVANCE: While experienced patellofemoral surgeons were able to identify femoral MPFL origin with reasonable accuracy by palpation, even experienced surgeons had inaccuracies that could compromise outcomes up to 18% of the time. For this reason we recommend the use of radiography along with appropriate exposure to assist in accurately identifying the anatomic femoral attachment of the MPFL during MPFL reconstruction.