Post-traumatic knee osteoarthritis with malunited regenerated distal femur and limb length discrepancy: A case report of computer-assisted navigation total knee arthroplasty

Abstract

This case report presents a challenging case of total knee arthroplasty (TKA) in a 65-year-old male with right knee tricompartmental post-traumatic osteoarthritis (OA), in a limb with a malunited regenerated distal femur reconstructed using Illizarov for segmental bone loss. The altered distal femoral anatomy poses a challenge for intramedullary rod referencing, necessitating the use of computer-assisted TKA. Through individualized preoperative planning and soft tissue-preserving techniques, accurate alignment, balanced gaps, and restoration of limb length were achieved without resorting to constrained implants and extra-articular osteotomy. Postoperative outcomes demonstrated a satisfactory range of motion, stable and well-aligned joint, complete pain relief, and full functional recovery. Radiographs confirmed the satisfactory limb alignment and component positioning. Despite the complexity of the case and altered anatomy, navigation enabled precise bone resections and balancing, emphasizing its role in complex primary TKA cases. To the best of our knowledge, this report is the first case to document TKA in a limb with a regenerated and malunited distal femur, providing insights into surgical planning and execution in such scenarios. Long-term follow-up is however necessary to evaluate the implant survival and complications such as periprosthetic fractures and infections.

1. Introduction

Total knee arthroplasty (TKA) in the setting of complex primary scenarios like a post-traumatic tricompartmental osteoarthritis (OA) complicated by a malunited distal femur presents significant surgical challenges,¹ which are further compounded when a segment in the lower femur is a regenerated bone. While there are reports describing TKA after distal femoral malunion and after Illizarov bone transport, to our knowledge, there is no reported case of TKA performed in a regenerated femur following distraction osteogenesis complicated by a malunion and with significant limb length discrepancy (LLD).

The challenges include²: surgical approach and exposure in the setting of tethered, scarred skin and compromised soft tissues with adhesions, difficulty in conventional intramedullary rod referencing, placement of navigation tracker pins with preexisting pin tracts, execution of precise bone resections, soft tissue balancing, accurate component positioning, risk of intraoperative periprosthetic fractures, periprosthetic joint infection, and restoration of leg lengths.

Such complex primary TKA cases demand meticulous preoperative planning, critical intraoperative decision-making, and precise execution of surgical steps. To the best of our knowledge, this report is the first case to describe the management of a complex primary TKA performed with Computer Assisted Surgery in a limb with a regenerated and malunited³ distal femur and advanced tricompartmental arthritis, highlighting key considerations and surgical techniques essential for a successful outcome.

2. Case presentation

2.1. Preoperative evaluation

A 65-year-old gentleman presented with chronic right knee pain for over sixteen years, progressive worsening of symptoms significantly impairing his functional abilities. He had a high-energy road traffic accident sixteen years prior, in which he sustained an open distal femur fracture with segmental bone loss, along with left tibia and right humerus fractures.

The right distal femoral fracture had been managed with multiple staged procedures, including debridement, bone transport, and reconstruction using the Illizarov technique, in the setting of infection and bone loss; the femur united in a mal-aligned position.

Clinically, the patient had no active sinuses over the right knee, and multiple healed surgical scars were noted over the anterior aspect. He had global joint line tenderness, varus deformity with painful flexion up to 90°. There was a 40 mm limb length discrepancy.

Radiographs revealed tricompartmental OA of the right knee with a distal femoral malunion (Fig. 1) and hip-knee-ankle (HKA) angle 10° degrees. Laboratory investigations, including inflammatory markers, and a diagnostic joint aspiration showed no evidence of infection.

Fig. 1.

Preoperative (a, b), postoperative (c, d) standing Anteroposterior (a, c) and lateral (b, d) knee radiographs.

Dotted lines in the (a, b) highlight the angulation and translation. (c, d) show correction of deformity and implant positioning.

The patient initially underwent trauma surgery and follow-up at another institution. He presented to us 16 years later when he experienced intractable pain and disability resulting from post-traumatic knee arthritis (Kellgren–Lawrence grade IV). At this advanced stage, he had failed all conservative treatment, and hence arthroplasty was indicated and offered for pain relief and functional restoration.

2.1.1. Preoperative planning

Preoperative planning involved a comprehensive evaluation of radiological parameters using long-leg scannogram, anteroposterior standing, lateral, and skyline knee radiographs. Key alignment indices including the HKA, mLDFA, MPTA, VCA, JLO, JCA, and TBA were carefully assessed to guide surgical decision-making. Anticipating intraoperative challenges, a posterior-stabilized prosthesis was selected as the primary implant option, with revision components kept on standby to address any unforeseen complexity during the procedure.⁴

Preoperatively, the patient managed the LLD with a large shoe raise. The main objective of surgery was to restore limb alignment and confer knee stability, pain-free motion, and function. Full correction of limb length was not pursued during knee replacement because adding a thicker polyethylene insert merely to reduce the discrepancy would compromise knee kinematics by stretching the collateral ligaments. Residual length discrepancy would require additional lengthening procedures which he could seek subsequently if he felt it was substantial. Therefore, we aimed for optimal joint reconstruction and counselled him that he may be left with minor LLD.

2.2. Intraoperative surgical steps

Summarized in Table 1.

Table 1.

Summary of Intraoperative Surgical Steps and navigation data.

Parameter	Details
Surgical Approach	Standard midline with medial parapatellar arthrotomy
Navigation System	Brainlab™ Knee3 Computer-Assisted Navigation was used due to significant femoral canal distortion (Fig. 1) and intramedullary referencing was not feasible
Infection Surveillance	Intraoperative frozen section, rapid molecular panel – Negative
Adhesiolysis	Extensive release of supra-patellar, medial, and lateral gutter fibrous adhesions
Pre-Resection Deformity	10° varus; correctible to 6° varus in extension; flexion limited to 90°
Gap Measurements	-In flexion (90°): Lateral 22 mm, Medial 14 mm -In extension: Lateral 11 mm, Medial 5 mm
Femoral Bone Cuts	-Distal femoral cut: 0.5° valgus to mechanical axis, 2° flexion, 6 mm, 0.5 mm thickness (medial, lateral condyles respectively) -Posterior condylar resection: 4.5 mm, 3.5 mm posteromedial and posterolateral cuts respectively using 2.5 femoral cutting block with 3.5° external rotation with respect to posterior condylar axis
Tibial Bone Cuts	1.5° varus to mechanical axis, 2° posterior slope, 6 mm, 4 mm resection of lateral and medial tibial plateau respectively
Trial Reduction	With size 2.5 femur and 12.5 mm spacer: Limb in extension 1° varus and 2.5° flexed; flexion to 106.5°; balanced gaps (<2 mm difference) in extension and flexion
Implant System	DePuy PFC SIGMA® Cemented Fixed-Bearing(….)
Components Used	-Posterior-stabilized femoral component -Metal-backed tibial baseplate -UHMWPE insert -Dome-type patellar component
Irrigation Protocol	Povidone-iodine, Hydrogen peroxide, Chlorhexidine, Vancomycin solution, Haemocoel

2.3. Postoperative course

On postoperative day 1, the patient had 0–100° range of motion (Fig. 2). The LLD was reduced from 40 mm pre-operatively to 15 mm, which was easily compensated by a shoe raise (Fig. 3), as evident in the long-leg radiographs (Fig. 4). Early mobilization and physiotherapy were initiated.

Fig. 2.

On postoperative Day 1: Clinical images showing the patient standing (a), sitting (b), and supine (c, d) during knee flexion (c) and extension (b, d).

Demonstrates good postoperative range of motion with no extensor lag.

Fig. 3.

Preoperative (a,b) and postoperative (c) shoe raise comparison for limb length discrepancy correction.

Note reduced shoe raise post-TKA following limb length restoration.

Fig. 4.

Preoperative (a) and postoperative (b) standing long-leg radiographs.

Demonstrates correction of limb alignment and restoration of limb length following total knee arthroplasty.

At 2 months, 6 months, and 1 year postoperatively, the patient demonstrated excellent functional recovery. He achieved independent, unassisted bipedal ambulation, had no signs of infection, and reported substantial pain relief with a stable and mobile knee joint. Early radiographs confirmed satisfactory component positioning and alignment.

The patient is now two years post–total knee arthroplasty (TKA) with a satisfactory functional outcome. The patient remains asymptomatic with respect to the TKA and has no knee-related complaints and is fully mobile.

3. Discussion

This case underscores the feasibility and effectiveness of performing primary TKA in complex post-traumatic scenarios involving extra-articular malunion and stiffness, using computer-assisted navigation.⁵ Despite the presence of a regenerated distal femur with residual deformity following distraction osteogenesis, the use of intra-articular releases combined with personalized, minimal bone resections allowed for satisfactory soft tissue balancing and component positioning. Notably, there was no requirement for additional extra-articular deformity correction or quadricepsplasty—underscoring the importance of the intraoperative value of computer-assisted navigation. The patient achieved satisfactory patellar tracking and quadriceps excursion due to extensive intra-articular releases and optimum component rotation.

For extra-articular complex knee deformities, there are three management options⁶: primary TKA, single-stage corrective osteotomy, and TKA, and a staged procedure⁷ where corrective osteotomy is followed by a later TKA. In this case, navigated posterior-stabilized primary TKA with asymmetric bone resection was employed as the HKA angle 10°, and collaterals were not compromised.⁸ and intra-articular correction enabled restoration of the neutral mechanical axis with optimum balance. Our approach demonstrates the feasibility of addressing malalignment and severe arthritis in a regenerated femur using a single-stage computer-assisted navigation TKA and not needing a staged procedure.

While there are no reported instances of TKA for malunited and regenerated distal femur with significant LLD, this case aligns with other reports^9,10 describing total knee arthroplasty for post-traumatic OA.

The optimal time for TKA after a bone regeneration procedure, when the regenerate is consolidated enough for full-weight bearing, is not clearly defined. This may be a subject for future research. It is prudent to consider TKA after sufficient remodelling of the regenerated bone segment. However, as sixteen years had elapsed in our case, this was not a consideration.

TKA in post-traumatic arthritis is generally associated with lower functional outcomes and implant survival compared to primary OA.¹¹ This is attributed to prior surgeries, altered anatomy, retained hardware, compromised soft tissues, and risks of latent infection.¹² Therefore, these cases demand a meticulous, individualized surgical strategy integrating advanced tools such as computer-assisted navigation¹³ or robotic assistance to optimize bone resections, alignment, and soft tissue balancing.

The potential long-term risks in this unique setting: (a) periprosthetic fracture through regenerated bone, (b) implant loosening given the altered biology of regenerated bone, and (c) theoretical risk of periprosthetic infection due to multiple previous surgical interventions. This case highlights a successful TKA in a limb with prior bone loss, distraction osteogenesis, and a malunited extra-articular deformity. Strengths include computer-assisted navigation and soft tissue-preserving techniques that avoid canal-based referencing, preserving bone stock. Long-term follow-up is warranted to evaluate implant survival and the risk of late infection.

4. Conclusion

This case highlights that with precise planning, intraoperative computer-assisted navigation, and adequate soft-tissue releases, complex primary TKA in post-traumatic knees with regenerated, malunited bone and extra-articular deformity can achieve excellent early functional outcomes without the need for constrained implants, extensive soft tissue reconstruction, and adjunct corrective osteotomy.

Consent

The manuscript is not submitted elsewhere for publication consideration. The patient gave consent for this case report to be written and published.

Ethical review committee statement

The study has been performed following the ethical standards in the Declaration of Helsinki.

CRediT authorship contribution statement

SC¹: Data Collection, Writing – original draft, Writing – review & editing.

ABM¹: Conceptualization, Supervision, Writing – review & editing.

RSM²: Writing - editing.

Funding statement

None.

Declaration of competing interest

None.