Bone autograft contains living cells that participate in the healing process. Fragmentation and heat production during cutting will kill cells. We have investigated how excessive graft fragmentation and heating can be avoided.

Two prototype cutters were fabricated. Each had a single cutting edge at the front end of a 12 mm diameter collection barrel. The principal difference between the cutters was the rake angle (at the cutting edge): 23° on cutter #1 and 45° on cutter #2.

Thrust load, feed-rate, and torque were measured using an instrumented drill press. A total of 58 tests on specimens of fresh bovine cancellous bone (distal femur, ex-abattoir) and medium density polyurethane foam (Sawbones, WA. USA) (density 252 kg/m³) were conducted: twenty-four at 100 rpm and thirty-four at 200 rpm.

Small flake-like fragmented bone chips were encountered at low thrust loads. As thrust load was increased the chips became thicker. The average cutting energy for bone was 43.7 Nm (s.d. 48.2 Nm) for cutter 1 and 37 Nm (s.d. 27 Nm) for cutter 2. The average cutting energy for the foam was 13.9 Nm (s.d. 6.0 Nm) for cutter 1 and 8.1 Nm (s.d. 3.0 Nm) for cutter 2. Polyurethane results showed a similar trend.

A higher rake angle on a bone graft tool is associated with a lower cutting energy. In turn, a lower cutting energy will generate a lower temperature in the graft, a result that is beneficial for cell survival. Graft tool design can also influence bone chip size. These experimental results are being used for the development of cell-friendly tooling.

Aim: To measure contact pressures in vivo in patients with unicompartmental arthritis fitted with osteoarthrosis (OA) braces to see if the arthritic side of the joint is unloaded.

Method: A thin flexible sensor (TekScan) was manoeuvered arthroscopically into the medial compartment of the knee joint under local anaesthesia in patients with unicompartmental OA of the knee undergoing either therapeutic or diagnostic arthroscopy. All 15 patients had been fitted with a brace before the arthroscopy. Measurements were made within the compartment of double leg stance and single leg stance. Ground reaction force using a load cell was measured for 14 patients and the knee sensor data were normalised relative to this. Recordings were then repeated with the patients with different commercially available braces.

Results: The first two groups of patients showed significant reductions in pressures. Normalised knee sensor forces were reduced to 68%(Sd 22%) and 61%(Sd31%). In the last group of patients, reductions in pressure recordings were less between no-brace and brace. Three patients produced low signals suggesting incorrect sensor replacement.

Conclusions:

Significant unloading of the osteoarthritic compartment could be observed by applying manually a valgus force to the knee.

Aim: To evaluate the technique of percutaneously harvested bone graft mixed with morphogenic bone protein and endoscopically delivered to ununited long bone fractures.

Methods: Thirty-eight patients with established delayed union of long bone fractures were bone-grafted endoscopically. Morphogenic bone protein (OP1) was used in 12 cases and the graft was supplemented with calcium sulphate pellets (Osteoset). The minimum follow-up was eight months. The study group included eight femoral shaft fractures, two humeral shaft fractures and the remainder were tibial shaft fractures.

Results: Four fractures failed to unite with this technique. Two femoral shaft non-unions required repeat surgery, one humeral shaft non-union and one tibial shaft non-union required supplementary grafting and fixation. The technique requires radiological imaging to supplement endoscopic preparation and graft delivery. For tibial fractures this can be used as a day-stay technique but most patients required one night in hospital.

Conclusions: Endoscopic bone grafting can be supplemented with graft substitute (Osteoset) and morphogenic protein (OP1). It is as effective as standard open ‘onlay’ grafting but good fixation of the fracture is necessary before graft and supplements are effective.