Gait analysis indicates increased abductor moment impulses two years after Ganz PAO

Harris hip scores improved 14 points and researchers noted that 11 of 15 hips had no pain.

Issue: June 2006

CHICAGO — Surgeons treating hip dysplasia patients with Ganz periacetabular osteotomies have relied on subjective measures to determine improvement in function. Now, a gait analysis study shows greater abductor moments at two-year postop.

Researchers from the Texas Scottish Rite Hospital for Children performed pre and postop gait analysis on 13 adolescent patients that underwent Ganz periacetabular osteotomies (PAO). They discovered a 0.3 N-m-sec/kg increase in hip abductor moment impulses two years after the procedure (P=.03). Yet, they found no significant difference in impulses at one-year postop.

“[This shows] us that the full benefit of the biomechanical improvement was not realized until two years,” Michael Wade Shrader, MD, an orthopedist at the Center for Orthopedic Research and Education in Phoenix, said during his presentation at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. Shrader, who conducted the research during his fellowship at the Texas hospital, said that the study constitutes one of the first to analyze gait changes after Ganz PAO.

The researchers also found better anatomical hip positions at follow-up. A radiographic analysis of the 15 hips showed that the mean lateral center edge (LCEA) and Tonnis (TA) angles significantly increased (both P<.001). The mean ventral center edge angle also improved by 31° (P=.0004).

In addition, “We had complete pain relief in eleven hips and improved pain with mild, residual pain in four hips,” Shrader said. The Harris Hip Scores (HHS) also increased 14 points (P=.001). “The study shows that in patients undergoing Ganz osteotomy, there were significant improvements in radiographic parameters for hip dysplasia, improvements in function by the Harris Hip Score and greater abductor moments,” Shrader said.

The researchers prospectively reviewed adolescent hip dysplasia patients treated with Ganz PAO between 1999 and 2004. “We excluded anyone that had hip dysplasia with any underlying neuromuscular diagnosis,” Schrader said.

The IRB-approved study included 14 females and one male with a mean age of 15 (the group ranged between 11 and 24 years old). A single surgeon performed all operations.

The investigators collected pre- and postoperative Harris Hip Scores and hip angles. They also calculated the lateralization ratio of the group. “We took the measurement of the symphysis pubis out to the center of the femoral head of the affected hip [then] we divided it by the contralateral hip,” Shrader said. “So that anything greater than one would show a lateral extension.”

They analyzed gait using a VICON motion system (Vicon Peak, an OMGplc company). The system included AMTI force plates, which assessed joint kinematics and kinetics. Besides contrasting the group's pre- and postoperative gait, the researchers compared the cohort's data with the movements of normal controls and followed the study group for a mean of 22 months.

Significant improvements

At one-year, patients’ hip abductor moment impulse increased from a preoperative value of 1.68 N-m-sec/kg to 1.76 N-m-sec/kg. “That was not significant, but by two years, they improved up to 1.98,” Shrader said. “And that was a significant improvement.”

Radiographic measures and patient reports also reflected improvement. The acetabular index decreased from 30° preop to 13° postop. The researchers found similar results for the CEA and VCEA. The CEA improved from –4° preoperatively to 23° postoperatively, while the VCEA increased from –2° to 23°. “Our lateralization ratio also improved from a value of 1.12 down to 1.04,” Shrader said. The patients also reported better hip function as Harris Hip Scores improved from 76 at preop to 90 at postop.

Limitations

Although the small cohort showed significant improvements, Shrader highlighted the study's potential selection bias. “Some of these patients were quite severe and had severe dysplasia, so you could consider this a salvage operation,” he said. “Also, I think our results show the severe learning curve of this difficult surgical technique and obviously we had small numbers.”

Shrader also noted that further studies are needed to explore long-term surgical effects. “We do feel that the Ganz PAO is a reliable treatment option for adolescents and young adults with symptomatic hip dysplasia, but obviously more investigation is needed to determine the long-term effects on the progression of arthritis and hip longevity,” he said.

For more information:
Shrader MW, Sucato DJ, Haideri N. Functional, gait and radiographic outcome following Ganz periacetabular osteotomy for hip dysplasia. #508. Presented at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting. March 22-26, 2006. Chicago.