Modified MCL indentationtechnique in total knee arthroplasty with severe type II valgus deformity

Purpose A modified technique, medial indentation of the medial collateral ligament(MCL),was usedin total kneearthroplastywith severe type II valgus deformity. The study compared the clinical outcomes of the technique relative to conventional release group. Consecutive patients with a Krackow type II valgus deformity of >20  who underwent a primary unilateral TKA between May 2008 and June 2017 were retrospectively studied.Modified MCL indentation technique was performed in 20 patients (group A), while the remaining 23 patients (group B) received routine release technique.Radiological parameters, such as the valgus angle (VA), and functional outcomes including the use of constraint implants, Knee Society Score(KSS), Knee Society function score(KSF), and height of the polyethylene insert, were compared between the two groups.


Introduction
Approximately 10% of patients with end-stage arthropathy who have undergone total knee arthroplasty have valgusdeformitiesof various degrees [1,2]. The valgus deformityis often accompanied by structural abnormalities of the bones and soft tissues, including contracture of the posterolateral joint capsule and lateral collateral ligament, relaxation of the medial collateral ligament (MCL), bone defect or dysplasia of the lateral femoral condyle, and bone defect ofthe tibial plateau. Krackow classifiedvalgus into three types, among which type II valgusis defined as combined with medial soft tissue laxity, so the deformities cannot be completely corrected [3].
Treatment of patients with type II valgus is exceptionally challenging. The valgus further aggravates the relaxation of the medial ligaments, especially in patients with severe valgus deformitywith a valgus angle of >20. Several reconstructive options can be used to address the soft tissue imbalance in patients with severe valgus deformitiestreated with TKA.
The first method is relatively simple and involves extensive release of the lateral structuresto match the medial side. If the medial-lateral balance cannot be achieved, constrained prostheses must be used [4]. The literature reports that although the mid-term clinical outcomes are satisfactory, the incidence rates of prosthesis loosening and instability increase [5]. In addition, comprehensive release of the lateral soft tissue resulted in utilizing thicker polyethylene insert, which would lead to the joint line changing and increase the possibility of common peroneal nerve injury.
Constrained prosthesis would not only increase cost, but make the possible future revision more difficult as well.The second method is the tightened suture of the medial ligament or upward restoration of the MCL tension [6]. However, the knee joint stability after applying this method depends on the healing condition of the MCL itself orits contact surface with bones. Moreover,significant residual valgusalongwith the lower limb's alignment after the operation may aggravate the relaxation of the medial side. Some authors have adopted upward sliding osteotomy of the medial epicondyle. However, the isotonic point of the ligament in flexion-extension gap balancing is not easy to determine during surgery, and the changesin theepicondylar axisof the femur may lead to long-term kinematic changes, so long-term follow-up of outcomes is needed. In addition, the third method is indentationthe insertion point of the MCL in situ. Krackow (1990) [7], Whiteside (1993) [8], and Healy (1998) [9] respectively reported this technique. The advantage lies in the indentation of theligament in situ without changing the epicondylar axis of the femur, and the lateral release can be reduced.Insert of standard thickness can be used without constrained prostheses, and excellentmid-term clinical outcomes have been achieved in all the cases.However,the cases may be small, with only 6-8 cases, and may have an unstable fixation of the advanced MCL just through making knot，therefore，existing arisk of long-term relaxation of the medial ligament. To optimize the fixation effect, we made some improvements to strengthen the fixation on the medial side.
This study's primary purpose was to investigate the clinical outcomes of the modified technique for medial indentationof the MCL.We hypothesized that for severe type II valgus deformity, the medial indentationof the MCL with PS arthroplasty would be as effective as routine releasegroup.The modifiedmedial indentation technique can achieve satisfactory mid-termoutcomesand reduce the use of constrained prostheses and thick polyethylene inserts, thus maintaining the normal joint line level.

Materials and Methods
This was a retrospective cohort study.

Eligibility criteria
Patients who had end-stage osteoarthritis of the knee with a Krackow type II valgus deformityof >20who underwent a primary total knee arthroplasty between May 2008 and June 2017 were considered for enrollment. The type of deformities, that is, the identification of medial laxity, was determined by a physical examination in which a gentle valgus force was manually applied on the knee in 20 flexion. The degree of deformities was measured preoperatively on a standing hip-knee-ankle radiograph.
Patients with neuromuscular disorders such as poliomyelitis and those without a minimum 2-year follow-up were excluded as well.

Study items
The baseline demographic information included age, sex, body mass index, diagnosis, and follow-up ( Figure 1). Radiographs used in this study included the hip-knee-ankle anteroposterior (AP) and lateral views, and Merchant patellar view of both knees.Valgus angle (VA) was defined as the angle between the femoral and tibial mechanical axes. The anatomical lateral distal femoral angle (aLDFA) was measured between the femoral anatomical axis and the tangent line of the femoral distal lateral condyle. The anatomical lateral plateau ankle angle(aLTPA) was the angle between the tangent line of the tibial plateau and the tibial anatomical axis [10]. The Insall-Salvati ratio of the knee was defined as described by Meneghini et al., for which a ratio between 0.8 and 1.5 was considered normal [11]. Outcomes were clinically evaluated using the Knee Society score (KSS) and Knee Society functional (KSF) score. Also, the polyethylene insert thickness, constrained implant use, and surgical complications were examined.
Study approval was obtained from the IRB of our hospital (ID:M2017106), and all the participants provided signed informed consent for surgery. (1) A preliminary limited lateral soft tissue release was performed, including the iliotibial band and posterolateral joint capsule, to the extent that the lateral space could accommodate the thinnest polyethylene insert ( Figure 2 ).
(2) The attachment of the MCL at the medial epicondyle was exposed. After drilling with a Kirschner wire, a miniature pendulum saw was used to open a window  (3) An interference screw (9mm×2.5 cm) was applied to strengthen the fixation at the window opening, a cortical bone screw was drilled into the external epicondyle of the femur, and suture thread was fixed on the bolt at its tail end (Figure 3).

Postoperative management
The drainage was withdrawn within 24 hours postoperatively. Low-molecular-weight heparin and foot-pump system were used to prevent deep vein thrombosis. The patients were immediately instructed to start static quadriceps and flexion-extension exercises. After drainage removal, the patients (Group A) were advised to perform active knee extension and straight-leg raise exercises with caution and then walkwith the toes touch or partial weight-bearingwith a long-leg knee brace removed after six weeks postoperatively.

Outcome evaluation
Surgical outcomes were evaluated clinically andradiologically, and compared between before operation, three months after the operation, 1 year after operation, and then annually thereafter.

Statistical analyses
The SPSS25.0 software was utilized for the statistical analysis. Measurement data conforming to a normal distribution are expressed as mean±standard deviation, a paired-samplest-test was used for intergroup comparison, and enumeration dataare expressed as rates. The difference was statistically significant whenthe P-value was <0.05.

Clinical Outcomes
The knees of all the patients in both groups were type II, according to Krackow the last follow-up.However, no statistically significant difference in preoperative or postoperative functional scores was foundbetween the two groups ( Figure 4). complications and, at the follow-up, said that she was delighted with surgery.

Complications
The complications of TKA were recorded in detail. One patient in the routine release group had the common peroneal nerve paralysis after the operation, decreased skin sensation on the dorsum pedis, and inability to perform ankle joint dorsiflexion. This might be related to the nerve traction after valgus correction and nerve traction injury caused by seed bone removal during operation. No special treatment was given, and the symptoms disappeared three months after the operation. One patient developed knee joint dislocation at 30 days after the operation and underwent revision with a thickened polyethylene insert. One patient had a periprosthetic fracture due to trauma one year after the operation and underwentinternal fixation. In the medial indentation group, one patient hadmedial knee joint instability, and the medial laxity exceeded 4mm during the valgus stress test. Considering that the MCL function was weakened, knee braceswere provided for protection, and the symptoms disappeared after three months. No complications such as infections, prosthesis loosening, and pulmonary embolism occurred during the follow-up period.

Discussion
The most important finding of this study is that for type II valgus with severe medial laxity, the MCL indentation technique is a safe and effective treatment method that can achieve satisfactory functions and maintain normal joint line level and reduce the use of CCK prostheses. Compared with the conventional operation group, the medial indentation group showed no statistically significant differences in KSS and KSF scores, with thinner polyethylene inserts, and had no common peroneal nerve paralysis. CCK inserts were used in asmaller proportion of patients in the medial indentation group than inthe conventional operation group(15% vs. 69.6%).
At present, no consensus has been reached on the treatment of type II valgus deformity [12,13]. Compared with that on the medial side of the knee, the controllability of the release on the lateral side of the knee is imperfect, owing to the lack of soft tissue sleeve. The extensive lateral release may lengthen the lateral structure, which will increase the risk of common peroneal nerve paralysis. A larger joint space will require thicker polyethylene, and a lower joint line will cause patella baja [14]. If the medial-lateral balance cannot be reached, instability on the medial side will often occur after surgery. If the correction is insufficient, residual valgus may also gradually aggravate the relaxation on the medial side [15]. Some authors believed that constrained condylar prostheses could well avoid this problem. However, the CCK prosthesis is semi-constrained [16,17]. The interface between the prosthesis and the bone cement bears great stress, and its postoperative loosening rate is high [18]. Pour et al. believed that the use of higher constrained prostheses such as hinged knees is associated with a high revision rate and relatively large bone defects during revision, which makesthe revision surgery difficult [19].
Reconstruction of the relaxed medial side is another option. Some authors considered folding the MCL or moving up its attachment point, but the stability of the knee joint after applying it depends on the healing of the MCL [6]. Moreover, if significantresidual valgusoccurs, it may aggravate the laxityon the medial side. The method of MCL indentation used in our research was first proposed by Krackow [3] andreported by Healy [9]and Whiteside [8]. Whiteside applied the MCL advancement method in 6 cases of valgusof >25. He believed that more bone in the distal femur would be cut off for the genicular lateral space to accommodate the prosthesis,and relaxation on the medial side will also increase. After theMCL indentation technique was applied, a 6-year follow-up did not show valgus recurrence orligament relaxation. the probability of using CCK will be decreased. The risk of common peroneal nerve injury is correspondingly reduced when the lateral release range is decreased. In this group of cases, nocases of common peroneal nerve paralysis were found, while one occurred in the control group. A bone-to-bone contact surface was attained with good bone healing potential after the medial ligament was tightened. The critical points of this technology are as follows: Carefully dissect theattachmentof the MCL, separate the bone blocks at the endpoint of the MCL using a miniature electric saw, and separate the two guide pins of the femoral condyle by 1cm to avoid cutting osteoporotic bone by the suture thread. Among the patients, one still had significant medial relaxation at six weeks after the operation and continued wearing brace protection for three months. This experience implies that if the overall lower limb alignment is corrected satisfactorily after the TKA and reached the neutral position, the relaxed medial ligament would gradually contract, and the instability would be improved accordingly.
Although this study is by far the largest cohort reported using this method, it still has some limitations, including the small number of cases and its retrospective nature. If themodified medial indentation technique is used,patients must wear braces for six weeks after surgery so that the recovery rate will slow down. However, for cases with a ruptured MCL or an accidental injury of the lateral collateral ligament during operation, this technique is not suitable, and the constrained prosthesis is still an effective rescuetreatment in such cases [20].