The Blackburne–Peel Index for Determining Patellar Height Is Affected by Tibial Slope

Abstract

Purpose: To establish a quantitative relationship between the BlackburneePeel index and posterior tibial slope in both skeletally mature and skeletally immature individuals and to evaluate the rate at which variation in tibial slope influences changes in patellar height categorization as normal, patella alta, and patella baja. Methods: A consecutive series of lateral knee radiographs were retrospectively reviewed. Radiographs were excluded for rotation, inadequate visible proximal tibia length, and obstructive hardware/pathology. Modified tibial slopes of 0 , 5 , 10 , and 15 were projected anteriorly from the medial tibial plateau as described by BlackburneePeel. The BlackburneePeel index was determined at each modified tibial slope interval. CatoneDeschamps and InsalleSalvati indices also were measured for comparison. The rate of BlackburneePeel index change with increase in posterior tibial slope was quantitatively analyzed. Results: Fifty skeletally mature and 50 skeletally immature radiographs were included. In the skeletally mature, BlackburneePeel indices decreased on average by 0.037, 0.044, and 0.049 as posterior tibial slope increased from 0-5 , 5-10 , and 10-15 , respectively. In the skeletally immature, BlackburneePeel indices decreased on average by 0.045, 0.053, and 0.059 as posterior tibial slope increased from 0-5 , 5-10 , and 10-15 , respectively. Overall, 29 individuals with 0 of tibial slope were categorized as patella alta by the BlackburneePeel index, and only 16 (55%) remained categorized as patella alta after increasing their posterior tibial slope to 15 . Conclusions: This study quantitatively demonstrates the relationship between posterior tibial slope and the BlackburneePeel index. As expected, as posterior tibial slope increases, the BlackburneePeel index decreases. While the change in the BlackburneePeel index per 5 change in tibial slope appears to be small, nearly half (45%) of individuals categorized as patella alta with 0 of tibial slope were categorized as normal when their posterior tibial slope was systematically increased from 0 to 15 . When evaluating patellar height, it is important to understand how tibial slope affects the Blackburne-Peel Index measurement. Clinical Relevance: As posterior tibial slope increases, the numerator of the Blackburne-Peel ratio decreases, and vice versa. This relationship can lead to incorrect assessment of patellar height. Objectively placing individuals into patella alta and baja categories may influence patient care and decision making. P atellar height is clinically relevant to several pathologic processes, including patellofemoral pain, chondromalacia, patellofemoral osteoarthritis, tibial tubercle apophysitis, patellar subluxation, and patellar dislocation. [1][2][3] Patellar height typically is assessed on lateral-view radiographs and sagittal plane imaging, and it is categorized as normal, patella alta, or patella baja. Patella alta describes a high-riding patella, whereas patella baja describes a low-riding patella.The InsalleSalvati inde...

Evaluation of proximodistal patellar alignment in small breed dogs with or without patellar luxation using the Insall-Salvati, Caton-Deschamps and Blackburne-Peel indices

“…The BPI is influenced by the tibial slope ( Mortensen et al ., 2021 )–increased tibial inclination reduces the BPI values, which is important for its interpretation both in humans and dogs from small breeds.…”

The Influence of Tibial Tubercle–Sparing Slope-Reducing Osteotomy on Patellar Height in Patients Undergoing Revision ACL Reconstruction

“…These results are, however, based on a simulated supratuberosity ACW osteotomy and account for the CDI only. Although a direct influence of PTS change on the BPI has been established, 37 the reliability of CDI and ISI may also be questioned after a slope-reducing osteotomy. In the current study, a significant postoperative change in FPHI was not identified; there was no influence of delta PTS on delta ( P = .3686) or ratio ( P = .3587) FPHI.…”

“…8 The Blackburne-Peel index (BPI) was not used in this study, as it is reported to be directly influenced by changes in the PTS, which may lead to an incorrect assessment of patellar height. 37 Given the concern that changes in PTS could inadvertently influence a tibial referenced technique, the femoral patellar height index (FPHI), a femoral referenced measurement technique, was also measured on frontal radiographs (Figure 4). 27 This index is defined by the ratio of the distance between the tangent line to the medial and lateral femoral epicondyles and the distance between the apex of the patella and the tangent line to the articular surface of the femoral condyles.…”

Anterior Closing-Wedge High Tibial Osteotomy Using Patient-Specific Cutting Guide in Chronic Anterior Cruciate Ligament–Deficient Knees

“…Thus, the Blackburne-Peel index has been proven to be directly affected by PTS. 35 Described in 2017, the femoral patellar height index is a femur-referenced patellar height measurement method avoiding HTO-related alterations of the proximal tibia. 36 This index could be useful to accurately measure the impact of ACW-HTO on patellar height.…”