Crowe Type IV Hip Dysplasia Treated by THA Comebined with Osteotomy to Balance Functional Leg Length Discrepancy: A Prospective Observational Study

Abstract

Objective: To measure the factors that affect functional leg length of Crowe type IV Developmental dysplasia of the hip (DDH) patients and to review our own methods to balance leg length discrepancy (LLD) in Crowe type IV DDH patients.

Methods: This was a prospective observational study which started in June 2017 and ended in August 2019. Inclusion criteria included: (i) Crowe type I or Crowe type IV hip dysplasia patients who underwent total hip arthroplasty (THA) in the Department of Orthopaedics at our institution between July 2017 and June 2018; (ii) the patients were treated with our specific leg length balance strategy; and (iii) the related outcomes of patients were completely recorded. Finally, 18 consecutive Crowe type I patients (20 hips) and 14 consecutive Crowe type IV patients (18 hips) were selected and divided into two groups according to Crowe types. All patients received THA, and patients with a longer affected side and inferior anatomical acetabular positions in Crowe type IV group also received subtrochanteric osteotomy. During operation and after hip reduction, leg lengths were compared while two legs were in an extended position and the operative leg was on top of the non-operative one. Additional leg length adjustment was applied when leg length was considered to be unequal. Prior to surgery, subluxation height of the femoral head on the affected side, functional LLD, bony length of lower limbs, and distance from teardrops to the lowest point line of the sacroiliac joint were recorded. After surgery, cup sizes, functional LLD, and height of hip rotational centers were measured. Clinical evaluations, such as Harris Hip Score (HHS) and SF-12 scale, were also obtained before and after surgery for all patients.

Results: At the last follow-up, functional LLD and clinical measurements of both Crowe type IV group and Crowe type I group were significantly improved. Compared with Crowe type I patients, Crowe type IV patients had a significantly lower MCS, a significantly longer leg lengthening length and a significantly lower hip center height after surgery. Significant differences of tibia length, leg length, and teardrop position were found between affected side and healthy side of Crowe type IV patients. Only three of 14 Crowe type IV patients remained under 1 cm functional LLD. Five patients in the Crowe type IV group developed lower limb numbness immediately following surgery, and they all recovered within 6 months. The average follow-up period for either group was 14 months, and all patients were followed-up at 1, 3, 6, and 12 months then yearly after surgery until the final follow-up.

Conclusion: After detailed leg length balance process, THA combined with transverse sub-trochanter osteotomy could be an effective method to achieve equal function leg length with most Crowe type IV patients.

Keywords: Hip dislocation; Leg length inequality; Osteotomy; Skeletal deformity; Total hip replacement.

Figure 1

Anteroposterior pelvic radiograph of two CROWE IV patients underwent THA with or without osteotomy. Pictures A and B belong to one patient underwent THA with osteotomy and pictures C and D belong to another patient underwent THA without osteotomy.

Figure 2

Schematic diagrams showing measurement of femoral head dislocation height, leg lengthening and hip center height. The transverse lines are teardrop lines. a and b are tips of lesser trochanters of two sides; c and e are tips of greater trochanter of affected side before and after THA respectively;d is the cup or femoral head center. Before surgery, femoral head dislocated height = aa' + bb'. After surgery, leg length lengthening = ee'−cc'. Used cup size was 40 mm, hip rotational center height = dd'.

Figure 3

A schematic diagram showing measurement of leg length. A is top of femoral head, B is midpoint of femoral condyles, C is inter‐condylar eminence of tibial, D and F are midpoints of the tibial plafonds, E is tip of lesser trochanter. Thus, AB is representative of femur length; CD is representative of tibial length; EF is representative for bony leg length.

Figure 4

A schematic diagram showing measurement of teardrop position. The transverse line in this diagram is the line that connected most inferior points of sacroilium joints, A and B are teardrops of affected side and healthy side respectively. Thus the two dash line vertical to the transverse line represent teardrop positions of two sides.

Figure 5

A series of plain X‐ray photographs of one Crowe IV patient received subtrochanter osteotomy. Picture A is an anteroposterior pelvic radiograph before surgery. Pictures B, C and D are of the positive and lateral radiographs of the hip joint at 3 days after surgery, 6 months after surgery and 1 year after surgery. Arrows represent that the osteotomy site is visible, and at 1 year after surgery, the osteotomy site is a bony union.