Prediction of loss of correction after hemiepiphysiodesis for the alignment of lower limb angular deformities

Abstract

Guided growth by temporary hemiepiphysiodesis (HEPD) is established for the alignment of lower limb angular deformities. This retrospective cohort study was designed to assess the effect of HEPD in idiopathic coronal plane deformities around the knee and on the frontal knee joint line orientation, and to test the frontal knee joint line as predictive means for recurrence.Fourty-four patients (78 deformities: valgus n = 64, varus n = 14) were enrolled in the retrospective observational study. Mechanical axis deviation, mechanical lateral distal femoral angle, and mechanical medial proximal tibial angle were assessed prior to surgery and during follow-up. The facultative frontal knee joint line angle (FKJLA) was used as predictive tool. Cases of remaining growth potential (n = 45/78) after implant removal were followed to assess rebound deformity.Pre-operative angles of the mechanical axis were corrected average 9.0 months after HEPD. Pre-operative assessment of the frontal knee joint line revealed a mean of 3.9° in valgus, and -1.0° in varus deformities. At time of complete deformity correction, mean FKJLA was -0.2° in valgus, and -0.8° in varus deformities. Mean shift of FKJLA was significantly higher after singleHEPD compared to combiHEPD (P < .001). Patients having an unphysiological FKJLA (>/<0°-3°) after correction of mechanical axis had a significantly higher risk of rebound deformity (P = .01). Regression analysis showed a 60.5% higher risk of rebound deformity per each degree deviating from the FKJLA physiological range. Age, gender, or body mass index had no impact.Temporary HEPD offers great potential for the correction of the mechanical axis and the frontal knee joint line. An unphysiological change of the frontal knee joint line is associated with a high risk of recurrent angular deformities. CombiHEPD instead of singleHEPD seems to be safer to prevent detrimental frontal knee joint line shift.Level of Evidence: Retrospective comparative therapeutic study, Level III.

Figure 1

FKJLA is defined as angle between the frontal center line of knee joints (FKJL) and the horizontal respectively the floor. Physiologically, the FKJLA is medially descending corresponding to a value of 0° to 3°, whereas a laterally descending FKJLA is pathological expressed as negative values. Graphics represent examples of + and −5° FKJLA.

Figure 2

Case of a 12 year old female with idiopathic genu valgum due to a pathologic mLDFA. The physis was located under an image intensifier (A, B). Skin incision was followed by dissection down to the periosteum. The physis was located again using a first guide wire. The appropriate plate size was selected and the plate was placed over the guide wire down to the bone. Prior plate bending was optional. Using the drill guide, both the epiphyseal and the metaphyseal guide wire was inserted (C). Correct positioning of the wires was checked using fluoroscopy (D). Cannulated screws were consecutively inserted as the growth plate must not be penetrated (E). Correct screw and plate positioning was finally checked using fluoroscopy (F). Guide wires were removed followed by wound closure. mLDFA = mechanical lateral distal femoral angle.

Figure 3

Box-and-whisker plots depict shift of mechanical axis deviation (MAD [mm]), tibiofemoral angle (TFA), mLDFA, and mMPTA (°) upon HEPD (pre-operative [blue] and prior to implant removal [green]) comparing valgus and varus deformities. Plots indicate variables outside the upper and lower quartiles, and outliers (^∗P < .05). Hatching displays anticipated physiological range of the mLDFA and the mMPTA. HEPD = hemiepiphysiodesis, mLDFA = mechanical lateral distal femoral angle, mMPTA = mechanical medial proximal tibial angle.

Figure 4

(Left) Mean shift of FKJLA (deltaFKJLA) was significantly higher (^∗P < .001) in the singleHEPD treatment group compared to combiHEPD. (Right) Deviation of FKJLA compared to an ideal value of 1.5° in patients with and without rebound deformity (loss of correction yes or no). Patients that ended up with an unphysiological FKJLA (>/<0°–3°) after correction of mechanical axis had a significantly higher (^∗P = .008) risk of developing a rebound deformity. HEPD = hemiepiphysiodesis, FKJLA = frontal knee joint line angle.