Characteristics of the patellofemoral joint of patients with DDH and the effects of Bernese periacetabular osteotomy on the patellofemoral joint

Abstract

Background: Some patients with developmental dysplasia of the hip (DDH) complained of anterior knee pain (AKP) before and after Bernese periacetabular osteotomy (PAO) surgery. The purpose of this study was to (1) identify the characteristics of patellofemoral joint (PFJ) deformities in patients with DDH and (2) to determine the effects of PAO on the PFJ.

Methods: Seventy patients (86 hips) were included in the DDH group. Thirty-three patients (33 knees) without AKP and hip pain were included in the control group. All patients underwent simultaneous CT scans of the hip and knee joints before PAO and after hardware removal surgery. The distance from the anterior inferior iliac spine to the ilioischial line (DAI), was measured in DDH patients. Imaging parameters of knees, including the sulcus angle (SA), femoral trochlear depth (FTD), patellar width (PW), tibial tuberosity-trochlear groove (TT-TG), patellar tilt angle (PTA) and lateral shift of the patella (LSP) were measured in patients in both the DDH and control group. TT-TG, PTA, and LSP of DDH patients were measured before PAO and after hardware removal. The DAI, PTA, LSP and TT-TG of all DDH patients before and after Bernese PAO were compared using paired t-tests. The FTD, PW, and SA of the DDH patients and the control group were analyzed using independent t-tests. PTA, TT-TG, and LSP between the control group and preoperative DDH patients, between the control group and post PAO patients were compared using independent t-tests.

Results: The DAI changed from 4.04 ± 0.61 mm before PAO surgery to 5.44 ± 0.63 mm after PAO surgery. The SA of the DDH group (140.69 ± 11.30 degree) was greater than that of the control group (130.82 ± 6.43 degree). The FTD and the PW of the DDH group (5.45 ± 1.59 mm, 4.16 ± 0.36 mm) were smaller than that of the control group (7.39 ± 1.20 mm, 4.24 ± 0.38 mm). The changes in LSP, PTA, and TT-TG before and after surgery were not statistically significant. Both before and after PAO, there was no statistically significant difference in the parameters of LSP, PTA, and TT-TG compared with the control group.

Conclusion: The knee joints of DDH patients presented a certain degree of femur trochlear groove dysplasia and patellofemoral instability. PAO surgery did not change PFJ stability, although the origination point of the rectus femoris muscle moved laterally during PAO surgery.

Keywords: Anterior knee pain; Bernese periacetabular osteotomy; Developmental dysplasia of the hip; Patellofemoral joint.

Fig. 1

A perpendicular line has been drawn from the AIIS to the iliac ischial line. The distance from the AIIS to the iliac ischial line was measured. The postoperative distance minus the preoperative distance is the displacement of the AIIS (DAIIS). AIIS: anterior inferior iliac spine

Fig. 2

A and B show the transverse sections passing through the largest femoral condyle. A illustrates the sulcus angle (SA). Two lines from the medial and lateral condyles to the deepest point of the intercondylar sulcus formed the SA. B illustrates the femoral trochlear depth (FTD). The distance from the deepest point of the femoral trochlear groove to the line connecting the most anterior points on the medial and lateral femur condyles is the FTD. C shows the transverse section passing through the midsection of the patella. The distance between the lateral and media of the patella is the patellar width (PW)

Fig. 3

Two transverse images were superimposed to measure the tibial tuberosity-trochlear groove (TT-TG) distance. The first transverse image that depicted a complete cartilaginous trochlea was adopted to determine the deepest point within the trochlear groove. The second transverse image shows the most anterior portion of the tibial tubercle. Line “a” is tangent to the posterior epicondyle. Line “b” goes through the deepest point of the trochlear groove, perpendicular to line “a”. Line “c” is parallel to line “b” and goes through the most anterior portion of the tibial tubercle. The TT-TG measurement is the distance between lines “b” and “c”

Fig. 4

Two transverse images were superimposed to measure the patellar tilt angle (PTA) and the lateral shift of the patella (LSP). The first image depicts the transverse section passing through the largest posterior femoral condyle. The second image shows the transverse section passing through the midsection of the patella. Line “a” is tangent to the posterior epicondyle. Line “b” goes through the horizontal axis of the patella. Line “c” goes through the medial point of the patella and is perpendicular to the line “a.” Line “d” is the perpendicular line from the apex of the medial femur condyle to line “a.” The angle formed by lines “a” and “b” is the PTA. The LSP is the distance between line “c” and line “d”