A Case Report of the Successful Conversion of One of the Longest Standing KineSpring Joint Unloading Systems.

INTRODUCTION: We present the case of a successful conversion of a KineSpring joint unloading system to a total knee replacement. This is, to the best of our knowledge, the so far longest surviving implant in Germany that has been successfully converted. CASE REPORT: The patient is a 75-year-old woman who presented to clinic with problems of her left knee. She had a KineSpring joint unloading system implanted in March 2011 for severe medial osteoarthritis of her left knee that was unresponsive to maximal conservative treatment. After nearly 7 pain-free years, we successfully converted the KineSpring joint unloading system into a total knee replacement (Vega, Aesculap, Germany).
CONCLUSION: The KineSpring joint unloading system is possible treatment option for younger patients with mild-to-moderate osteoarthritis of the knee reluctant to total knee replacement, without compromising further surgical options.

Learning Point for the Article:

The KineSpring joint unloading system is possible treatment option for younger patients with mild to moderate osteoarthritis of the knee reluctant to total knee replacement, without compromising further surgical options

Introduction

We present the case of a successful conversion of a KineSpring joint unloading system to a total knee replacement. This is, to the best of our knowledge, the so far longest surviving implant in Germany that has been successfully converted. Osteoarthritis of the knee is a degenerative disease affecting approximately13% of females and 10% of males aged 60 years and older [1]. Due to demographic changes and an increase in physical activity even in an older population, the incidence of knee osteoarthritis is rising. Early phase knee osteoarthritis is often limited to a single compartment. The medial compartment bears over two-thirds of the load acting on the knee during normal gait, consequently, increasing the risk of this compartment to joint degeneration [2,3]. The knee adduction moment, a well-known indicator of maximum joint load in the medial compartment endured during normal gait, is higher in patients with knee osteoarthritis compared to a healthy population [4, 5]. Chronic excess joint loading is associated with greater osteoarthritic pain severity and faster disease progression [6, 7, 8]. Unloading of the medial compartment may improve knee osteoarthritic symptoms and slow down disease progression by providing a local mechanical environment that encourages articular cartilage healing [4, 9]. Many conservative treatments, for example, lateral wedge insoles and valgus knee braces, aim to reduce medial knee compartment joint loading forces. Unfortunately, long-term effect of conservative treatment patterns is often poor largely due to the patient compliance challenges [10,11]. The KineSpring Knee Implant System (Moximed Inc., Hayward, CA, USA) is an implantable extra-articular, extracapsular prosthesis intended to alleviate knee osteoarthritis symptoms by reducing medial knee compartment loading while overcoming the limitations of traditional joint unloading therapies [4]. This device consists of two base plates, one fixed to the distal femur and the other one to the proximal tibia with an absorber piece in between (Fig. 1). This reduces the load on the knee up to 30 lbs during full extension and is designed primarily for patients with mild-to-moderate knee osteoarthritis [4]. Several case series examined the effectiveness of the KineSpring system and demonstrated the longitudinal positive outcomes with follow-up periods of 5 years [12]. The presented study reports a case of a patient who underwent successful conversion of the KineSpring system to a total knee replacement nearly 7years after implantation of the KineSpring system.

Figure 1

Components of the KineSpring System. (a) Femoral base, (b) absorber, and (c) tibial base. Reproduced with permission from Moximed.

Case Report

The patient is a 75-year-old woman who presented to clinic with problems of her left knee. She had a KineSpring joint unloading system implanted in November 2011 for severe medial osteoarthritis of her left knee that was unresponsive to maximal conservative treatment (Fig. 2 and 3). The KineSpring procedure followed standard techniques that have already been described [10]. The patient remained hospitalized for 3 days following the procedure. She reported immediate arthritic pain relief postoperatively. For more than 6 years, she remained pain free and the KineSpring joint unloading system functioned well. At the end of October 2017, the patient presented to clinic with increasing the left knee pain. She reported increasing pain with weight-bearing and knee flexion and had been taking anti-inflammatory medication as needed. The knee was stable in varus and valgus testing, although testing was ratherdifficult due to the KineSpring implant. Radiographically, there were signs of a severe osteoarthritis of the lateral and the patellofemoral compartment (Fig. 4 and 5). In November 2017, the patient underwent conversion of the KineSpring system to a total knee replacement (Vega Femur Size 5 narrow, Columbus Tibia Size 2, PE-Inlay PS 12 mm, Aesculap, Germany). The procedure was performed without any difficulties. Removement of the KineSpring system added an additional 11 min to the operation time. Implementation of the Columbus total knee replacement (Aesculap, Germany) followed our standard techniques and was not complicated by the former KineSpring system. Post-operative radiographs showed that the femoral and tibial implants were placed properly (Fig. 6 and 7). Post-operative course was good, and the patient was discharged 10days postoperatively to rehabilitation. 3months after surgery, she is pain free, mobilizing without any walking aid and with a more than satisfactory range of motion of her left knee.

Figure 2

X-ray of the left knee AP before the KineSpring procedure.

Figure 3

X-ray of the left knee lat. before the KineSpring procedure.

Figure 4

X-ray (AP) of the left knee 7 years after implantation of the KineSpring system.

Figure 5

X-ray (lat.) of the left knee 7 years after implantation of the KineSpring system.

Figure 6

X-ray of the left knee (AP) after 2 days successful conversion to a total knee replacement

Figure 7

X-ray of the left knee (lat.) after 2 days successful conversion to a total knee replacement.

Discussion

In this case report, we describe the successful conversion of a KineSpring joint unloading system to a total knee replacement. Excessive mechanical stress across the knee joint leads to the onset and progression of knee osteoarthritis [13,14]. A change of the adverse biomechanics that produced the predisposing conditions for osteoarthritis is a key to provide lasting relief from symptoms and to slow down progression of knee osteoarthritis [3,15]. A gait simulation study demonstrated that KineSpring can successfully unload the medial compartment of the knee [16]. Unlike high tibial osteotomy, the KineSpring procedure does not involve significant bone removal and reshaping in an effort to shift loading from the affected to the unaffected compartment. High tibial osteotomy is a very invasive surgery, requiring an average of approximately 10 days of post-operative hospitalization [17]. A substantial delay in return to work of typically 3 months has been described [18]. Significant procedural risks, such as infection, thrombosis, delayed or non-union, and peroneal nerve lesion, limit the utility of high tibial osteotomy [19]. Due to these reasons, many patients refuse to undergo high tibial osteotomy although they were unresponsive to conservative treatments. Furthermore, many patients are not willing to consider total knee replacement due to the invasiveness of the procedure, extended recovery period, and complication risk [20]. As a result, approximately 3.6 million patients with osteoarthritis of the knee in the United States alone linger in a treatment gap, characterized by failure of conservative treatment, and refusal to undergo total knee replacement [11]. For these patients, the KineSpring system is an option to fill this therapeutic gap. Key component of the KineSpring implant is a cobalt/cobalt-chrome alloy absorber with the ability to reduce the load in the affected medial compartment during gait by up to 13 kg [21]. The absorber resides in the subcutaneous tissue and is attached to titanium alloy femoral and tibial bases. The KineSpring system is extracapsular and extra-articular with no removal of bone, ligament, or cartilage required [21]. Despite the simplicity of the implantation, surgeons must be familiar with appropriate revision techniques. Further, treatment options may not be compromised by the KineSpring system. We successfully converted one of the longest standing KineSpring joint unloading systems into a total knee replacement. The explanation of the absorber system was easily done, without complicating the standard procedure of total knee replacement. After the primary implantation of the KineSpring absorber, our patient was pain free for nearly 7 years, enjoying her daily life. Consequently, the KineSpring is an alternative treatment for mild-to-moderate osteoarthritis of the knee, especially for younger patients reluctant to more invasive procedures.

Conclusion

With this case report, we were able to show that the KineSpring joint unloading system is an easily reversible procedure that maintains the anatomical integrity of the knee joint, enabling orthopedic surgeons to help patients with medial osteoarthritic knee pain and reluctance to undergo total knee replacement. In our case, the patient gained 6 pain-free years before a total knee replacement was performed. We showed that explanation of the KineSpring system was safe and easy, without compromising further surgical options like total knee replacement. In sum, we can say the KineSpring joint unloading system is not the substitute of total knee arthroplasty, but a temporary option.

Clinical Message

The KineSpring joint uploading system is a possible treatment option for younger patients with mild-to-moderate osteoarthritis of the knee reluctant to total knee replacement, withoutcompromising fruitful surgical outcomes with other options.