Combination of external fixation using digital six-axis fixator and internal fixation to treat severe complex knee deformity

Abstract

Background: Severe knee valgus/varus or complex multiplanar deformities are common in clinic. If not corrected in time, cartilage wear will be aggravated and initiate the osteoarthritis due to lower limb malalignment. Internal fixation is unable to correct severe complex deformities, especially when combined with lower limb discrepancy (LLD). Based on the self-designed digital six-axis external fixator Q spatial fixator (QSF), which can correct complex multiplanar deformities without changing structures, accuracy of correction can be improved significantly.

Methods: This retrospective study included 24 patients who suffered from complex knee deformity with LLD treated by QSF and internal fixation at our institution from January 2018 to February 2021. All patients had a closing wedge distal femoral osteotomy with internal fixation for immediate correction and high tibia osteotomy with QSF fixation for postoperative progressive correction. Data of correction prescriptions were computed by software from postoperative CT scans.

Results: Mean discrepancy length of operative side was 2.39 ± 1.04 cm (range 0.9-4.4 cm) preoperatively. The mean difference of lower limb was 0.32 ± 0.13 cm (range 0.11-0.58 cm) postoperatively. The length of limb correction had significant difference (p < 0.05). The mean MAD and HKA decreased significantly (p < 0.05), and the mean MPTA and LDFA increased significantly (p < 0.05). There were significant increase (p < 0.05) in the AKSS-O, AKSS-F and Tegner Activity Score. The lower limb alignment was corrected (p < 0.05). The mean time of removing external fixator was 112.8 ± 17.9 days (range 83-147 days).

Conclusions: Complex knee deformity with LLD can be treated by six-axis external fixator with internal fixation without total knee arthroplasty. Lower limb malalignment and discrepancy can be corrected precisely and effectively by this approach.

Keywords: Knee; Osteotomy; Q spatial fixator (QSF); Valgus; Varus.

Fig. 1

The picture of six-axis Q spatial frame (QSF). It is constructed by two rings and 6 struts. There is a nut on the strut to be screwed to lengthen or shorten the strut. Two kinds of pins are used which are Kirschner pins and Schanz pins. Pins are fixed onto the rings by clamps and conjunction parts. The nut has six facets. The lengths of strut will change 1 mm when the nut is screwed one round

Fig. 2

The measurement of lower limb discrepancy and alignment. Lower limb discrepancy was measured by the sum of femur length and tibia length, and the low alignment was measured by HKA

Fig. 3

An 18-year-old patient had bilateral knee and malleolus valgus because of multiple osteochondroma. The right lower limb was 3.3 cm shorter than the left. a Full-length radiograph before operation. b X-ray after operation shows the deformity has been corrected. c Left lower limb surgery will be taken after 1 year. d Osteotomy and internal fixation at the left side. Re-examination X-ray shows the osteotomy site healed well. The lower limb alignment of right limb and the LLD is near normal

Fig. 4

An 18-year-old patient had right varus knee because of Blount disease. The right lower limb was 2 cm shorter than the left. a Full-length radiograph before operation. b X-ray after operation shows DFO was, and QSF was applied. Re-examination X-ray shows the osteotomy site healed well, and the QSF was removed. The lower limb alignment of right limb and the LLD is near normal