UTRECHT, Netherlands–A relatively brief period of joint distraction might permit patients with knee osteoarthritis (OA) to delay or even avoid total knee replacement and should be studied in a prolonged, prospective multicenter study, according to Anne C. A. Marijnissen, PhD, Floris P. J. G. Lafeber, PhD, and colleagues at University Medical Center, Utrecht, Netherlands.¹ Drs. Lafeber and Marijnissen presented data on the first 7 patients from this group's knee OA study at the 2006 European League Against Rheumatism (EULAR) meeting.^1,2 Previous work by this group had shown sustained benefits for many patients with ankle OA.³

Joint distraction uses an external fixation frame [see Figure 1] to relieve mechanical loading of the periarticular bone, reduce mechanical stresses on the joint cartilage, prevent further wear and tear of the cartilage surfaces, and give chondrocytes a chance to begin repair. Distraction has been studied for treatment of ankle OA, particularly posttraumatic OA, and this group recently reported follow-up data showing that 2 months of joint distraction produced significant clinical benefit lasting more than 7 years in patients with severe OA of the tibiotalar joint.³

^{Figure 1. Different examples of joint distraction in the
 treatment of osteoarthritis}
 

(a) Hinged, articulated hip distraction. Reproduced with
permission from Aldegheri et al. [41]. (b) llizarov ankle
distraction using thin wires. Reproduced with
permission from van Valburg et al. [42]. (c) Knee
distraction using an Howmedica system with springs.
Kindly provided by A.C.A. Marijnissen.
Reprinted from Current Opinion in Rheumatology. Used

with permission.

The knee distraction device consists of two external Howmedica fixation tubes (with springs) that bridge the knee joint. They are placed on pins drilled through the patient's soft tissue into the bone above and below the knee. The distraction of the knee is then increased by about 0.5 mm per day until radiographic monitoring shows a distance of 5 mm.

"Intra-articular fluid pressure changes, expected to be required for nutrition of the cartilage, were measured in the joint during distraction. The required absence of mechanical load on the cartilage, preventing further wear and tear, was controlled on standardized radiographs," Dr. Marijnissen said.

Study endpoints were pain functional disability, clinical condition, and flexion of the treated knee.

The investigators found that mean intra-articular fluid pressure was 1.1 kPa during relaxation and 9.2 kPa during loading. Distraction eliminated mechanical load on the knee cartilage.

The duration of joint distraction required to promote cartilage healing has been a subject of debate. Half the patients in this study were treated for 3 months, the other half for 2 months, and the investigators reported that 2 months was as effective as was treatment of longer duration.

Dr. Marijnissen reported that at 1 year post surgery, pain decreased from 75% of the maximum score to 14%. Disability decreased from 64% to 7% of the maximum score. Clinical condition improved from 34% to 88% of the maximum. Knee flexion remained normal.

The improvements also were durable. The first three patients treated are now 2 years post surgery, and Dr. Marijnissen said that clinical efficacy has persisted during the second year.

The result is likely also to have economic consequences. The Dutch researchers estimate that joint distraction for knee OA costs 1500 euros less than knee replacement surgery.

In a separate presentation at EULAR, Dr. Lafeber reviewed the group's work on joint distraction in ankle OA and discussed current thinking on underlying mechanisms of action. In addition to preventing additional wear and tear of cartilage, allowing chondrocytes to initiate repair, and maintaining chondrocyte nutrition by intermittent fluid pressure in the joint, joint distraction elicits changes in subchondral bone.

"Distraction relieves mechanical loading of periarticular bone, leading to temporary osteopenia within the distraction area. Turnover of bone, being a large storage of growth factors known to be involved in cartilage growth and repair, may provide support to chondrocytes in a cartilage repair mode. After distraction, less dense subchondral bone will absorb greater stress, and with that, lower the stress on overlying cartilage," Dr. Lafeber said.

Another interesting aspect of this process is that clinical improvement may continue to increase over a considerable time after the period of distraction treatment. In a study of joint distraction for treatment of ankle OA in patients who were otherwise candidates for joint fusion, Dr. Marijnissen found that pain and function were significantly better at 1 year post surgery, and were significantly better after 3 years compared with 1 year.⁴

The researchers point out that joint distraction might buy considerable time for OA patients who would otherwise be headed for joint replacement or ankle fusion. This possibility assumes major importance for younger patients such as those with posttraumatic OA in view of the limited lifespan of implants and the "frequently disappointing" results of revision surgery, they write.⁴

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