Total knee arthroplasty (TKA) is a reliable surgical option in the management of end-stage osteoarthritis of the knee. Posterior-stabilized (PS) designs are one of the most widely used prosthetic designs in TKA. The first PS prosthesis was designed by Insall and Burstein ^[1]. The PS-TKA design compensates for the absent PCL with a cam post-mechanism. The tibial post of the PS polyethylene insert engages the cam of the femoral component to prevent posterior subluxation of the tibia under the femur. The intricacies that are distinctly linked to the design of PS-TKA implants encompass a range of potential complications, primarily manifested in the patellofemoral joint. These complications may manifest as the patella clunk syndrome or crepitus, both of which can impede the optimal functionality of the implant system ^[2]. In addition, complexities can arise in connection to the post and cam mechanism, giving rise to issues such as tibial post-wear, impingement, or even fracture, as substantiated by reference ^[3]. Notably, an assortment of case reports has reported both traumatic and non-traumatic fractures of the tibial post, without any documented rate of tibial post-attrition in literature. We present an unusual case of prosthetic failure with a completely eroded tibial post and provide a review of the literature regarding the commonly elicited causes of erosion and treatment options for such complications.

A 73-year-old female presented to our outpatient department with a complaint of left knee pain and instability while walking, over a duration of 1 year. This patient had undergone primary TKA 5 years before presentation at a different center for primary OA of the knee. She was operated with a PS knee design (Maxx Destiknee, Meril, Vapi, India). This cemented PS prosthesis has an ODEP rating of 5B. The patient had a well-functioning joint for 4 years after the primary surgery and was ambulating without aid or pain and was able to perform all ADLs independently. 12 months before presentation, she started experiencing pain which was insidious in onset and gradually progressive and noticed instability while walking 2–3 months after the onset of pain. Clinical examination revealed a well-healed midline scar without local signs of infection or inflammation. Clinical examination showed a knee effusion, with diffuse and mild tenderness over the anterior knee. Her knee range of motion was from −20° hyper-extension to 100° of flexion. The valgus stress test was positive (grade 2) and the anterior draw was >5 mm, suggesting instability in both the coronal and sagittal planes. She did not have any neurovascular deficit. Plain radiographs did not reveal obvious osteolysis or component loosening. The tibial base plate showed mild valgus alignment.

The tibial component appeared undersized with bone beyond the lateral edge of the baseplate (Fig. 1a). Valgus stress radiograph revealed medial extension laxity (Fig. 1b). Notable laboratories on admission included a white blood count of 10 K/µL, erythrocyte sedimentation rate of 60 mm/h, and C-reactive protein of 8.3 mg/L. Considering the marginally elevated inflammatory markers and a clinically relevant knee effusion, her knee was aspirated. Synovial fluid analysis showed clear fluid with normal cell counts. The gram and acid–fast staining and routine cultures were all negative. Based on these findings and her clinical picture, the patient was advised aseptic revision surgery. Revision surgery was carried out using a standard medial parapatellar approach.

Before beginning the revision procedure, the knee recurvatum and valgus opening were assessed and demonstrated intraoperatively (Fig. 2a and b). After the completion of the arthrotomy, the polyethylene tibial post was missing and was not located within the knee joint cavity (Fig. 3a). There were no signs of infection. The polyethylene insert was removed and noted to have evidence of polyethylene wear, with clear evidence of delamination and striping in the location of the tibial post. (Fig. 3b) both the femoral and tibial components were well fixed, and the surgeon tried to address the instability with a thicker insert (17 mm maximum PS insert available). However, the knee was still lax, with an incompetent MCL. Subsequently, the decision was taken to proceed with a complete revision arthroplasty with a rotating hinge prosthesis.

The surgeon implanted the DePuy (DePuy Synthes, J and J, Warsaw, USA) Noiles rotating hinge knee. The trial hinge components gave the surgeon good biplanar stability and knee ROM. The components were cemented and tourniquet deflated. The immediate post-operative X-ray is shown in (Fig. 4). The patient was allowed to fully bear weight on the 1^st post-operative day, without knee range of motion restrictions. At the most recent follow-up of 12 months, the patient is walking without pain or instability, has no wound-healing complications, and active ROM of 0–100°.

PS prosthetic designs represent a prevailing choice for TKA. These designs incorporate a cam post-mechanism to replace the function of the posterior cruciate ligament, effectively preventing posterior subluxation of the tibia under the femur during knee flexion and promoting improved femoral rollback and knee flexion ^[4,5]. Wear and failure of the tibial post have been documented in previous studies ^[6,7,8,9,10] (Table 1).

Several causative factors have been proposed for tibial post-wear and erosion:

1. An increased posterior slope of the tibial baseplate may lead to premature and suboptimal femoral contact with the post.
2. Femoral rotation can induce edge loading on non-rounded posts and cams, thereby contributing to tibial post-failure.
3. Excessive flexion of the femoral component may result in cam post-impingement.
4. Post-cam engagement velocity and flexion engagement angle under dynamic physiological conditions also play a role in wear ^[11]. Severe cases have shown complete erosion of the tibial post, while another rare yet significant complication is tibial post-fracture due to wear and deformation, occurring in <1% of cases ^{[12,13,14,15]}.

Addressing tibial post-related complications typically necessitates case-specific treatment, often involving polyethylene liner exchange to a thicker insert ^[12]. Bal et al. have demonstrated promising short-term results in 18 knees following polyethylene exchange to address this issue ^[16]. Moreover, some researchers have noted that revising components with increased constraint to manage persistent coronal instability can yield improved short-term outcomes ^{[13,15,17,18]}. As illustrated in this case report, tibial post-failure post-TKA can manifest without an overt history of trauma or falls. Such failure may arise from either traumatic or non-traumatic causes. In cases where progressive instability presents without a history of trauma, surgeons should consider the possibility of polyethylene wear-related failure. Revision surgery, involving a complete component revision as necessary, should be diligently planned, as the chronic and progressive nature of failure results in significant joint laxity that cannot be adequately addressed by polyethylene exchange alone.

Surgeons must be cognizant of the various prosthetic failure mechanisms that can occur after TKA. PS-TKA designs are susceptible to unique failure mechanisms, such as the disruption of the cam post-mechanism. The tibial post may fracture in acutely (traumatically) or chronically (atraumatically). The patient’s clinical history can assist surgeons in diagnosing these issues. Pre-revision imaging with advanced modalities such as computed tomography (CT) or magnetic resonance imaging (MRI) can facilitate surgical planning.

Surgeons should be aware of all possible prosthetic failure mechanisms after TKA. PS-TKA designs have unique failure mechanisms, including failure of the cam post-mechanism. Tibial post-failure can be acute (traumatic) or chronic (atraumatic) and obtaining a good clinical history will help guide surgeons in diagnosing these issues. Pre-revision imaging with advanced imaging modalities such as CT or MRI may be helpful in planning revision surgery.