Alignment Key To Knee Surgery Success; Even Small Degree Of Bow-Leggedness Can Lead To Degeneration Of Knee Joint After Surgery

Even a small "varus knee malalignment" -- more commonly known as bow-leggedness -- can lead to serious future problems for knee surgery patients, the researchers said. They added that physicians should at minimum closely monitor all young people who undergo reconstructive knee surgery to ensure that the leg bones stay in proper alignment, and in some cases surgically correct the bowleggedness. They see such strategy a possible preventative measure against the future development of severe arthritis of the knee.

"Even a relatively small malalignment in normal knees can cause dramatic alterations in the pressures within the knee joint, and this negative effect can be greatly magnified if the cartilage within the knee has been damaged," said Joseph Guettler, M.D., orthopedic surgeon and sports medicine fellow at Duke. "With early recognition and intervention of the malalignment, we can perhaps prevent the development of serious osteoarthritis from occurring in the future."

Guettler conducted a study whose results were prepared for presentation today (July 3, 2002) at the 28th annual meeting of the American Orthopedic Society for Sports Medicine (AOSSM). The study received the 2002 Herodicus Award, given annually by Herodicus Society at the AOSSM meeting for the best paper submitted by an orthopedic resident or sports medicine fellow.

The Duke researchers sought to characterize the effects of malalignment on the knee joints of patients who had suffered damage to the cartilage within the knee. Specifically, they analyzed the pressures within the knee joint over the cartilage after the creation of a defect in the cartilage and removal of the meniscus. The meniscus is a piece of fibrous cartilage within the knee that acts as a cushion or "shock absorber."

For their studies, the Duke team placed eight cadaveric human knees in an apparatus that creates loading across the knee joint. They then used the latest technology to measure pressures over the cartilage within the knee joint.

The researchers found that even three degrees of malalignment, which can only be detected by X-ray, can lead to profound deformation of the cartilage. For example, this small deviation more than doubled pressures on the middle of the knee joint, and peak contact pressures increased 68 percent. Over time, these uneven pressures within the joint lead to uneven wear and tear, which leads to painful and often debilitating osteoarthritis.

"Past studies have shown that between 20 and 50 percent of patients who have had significant knee cartilage damage developed severe arthritis," Guettler explained. "What hasn't been shown is why some patients do and some do not. Our studies would suggest that a very important factor is the subtle changes in alignment of the leg bones relative to the joint and the pressures they place on the cartilage within the knee."

For patients who have significant cartilage damage or have had damaged cartilage removed, Guettler recommends that very close attention be paid to the alignment. These patients should be followed very closely, and if any clinical or X-ray evidence of deterioration occurs, an operation known as an osteotomy should be considered. This surgical procedure involves taking a wedge-shaped piece of bone out of the leg, in essence changing someone from being bow-legged to being knock-kneed. This over-compensation relieves the pressure on damaged parts of the knee and transfers it to undamaged areas.

"In these cases, the surgery is seen more as a preventative measure against future osteoarthritis, as opposed to a treatment for a specific disorder," Guettler said. "This is an invasive procedure with known complications, yet it should be considered for these high-risk patients."

Timing is the key consideration for this procedure, Guettler said. The osteotomy is usually reserved for someone in middle age who already has developed significant osteoarthritis. Based on the results of this study, an osteotomy would be recommended in a predominantly younger population. It may, however, be more difficult for the parent of an injured 18-year-old to make such a decision, since the teen-ager would not see the benefits until decades later, Guettler said.

Guettler said that as new surgical procedures -- such as meniscus transplants or the implantation of cartilage grown outside the body -- gain widespread use for patients with knee injuries, physicians should pay close attention to alignment, since it plays an important role in the ultimate success of the procedure.

The other members of the Duke teams were Richard Glisson, Alston Stubbs, M.D., Kenneth Jurist, M.D. and Laurence Higgins, M.D. The research was supported by Duke Sports Medicine.