Knee Arthroplasty Treatment – Case Presentations and Discussion

Archival Presentation Notice: This article modernizes the multimedia presentation “Knee Arthroplasty Treatment – Case Presentations and Discussion” originally presented by Prof. Jean-Noël Argenson, MD, PhD (Aix-Marseille University). The historical Flash lecture has been reconstructed into the synchronized video slide presentation above, with the original file preserved in the digital archives (Argenson_new_arthritic_Case_Discussion.swf).

1. High-Yield Summary

• The Young, Active Arthritic Dilemma: Clinical presentation of a 56-year-old active male with isolated medial compartment knee osteoarthritis embodies the classic reconstructive crossroads between High Tibial Osteotomy (HTO), Unicompartmental Knee Arthroplasty (UKA), and Total Knee Arthroplasty (TKA).
• Evolution Beyond Kozinn & Scott: Historical restrictions excluding patients younger than 60 years or engaged in athletic activities have been superseded by modern clinical evidence; patient selection hinges on compartmental disease isolation, ligamentous integrity, and correctability of deformity rather than chronologic age alone.
• Cruciate and Kinematic Preservation: Both UKA and HTO retain the native anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), preserving physiologic screw-home mechanics, normal proprioception, and physiological knee kinematics that yield substantially higher “forgotten joint” scores than conventional TKA.
• Essential Diagnostic Quadrad: Preoperative evaluation strictly requires bilateral full-length standing weight-bearing teleoroentgenograms (mechanical axis), true AP, 45° flexion posteroanterior Rosenberg views (unmasking posteromedial joint space loss), and sunrise Merchant views at 30°, 60°, and 90° (confirming patellofemoral compartment preservation).
• The Overcorrection Hazard: In medial UKA, correcting the mechanical axis into valgus transfers destructive loads to the uninvolved lateral compartment, precipitating rapid arthritic deterioration; the surgical goal is undercorrection that restores pre-morbid joint line height while leaving constitutional varus (2° to 4°) intact.

2. Anatomic Compartments and Joint Biomechanics

Formulating an optimal surgical strategy for localized gonarthrosis demands an appreciation of compartmental load sharing, native knee ligamentous restraints, and lower-limb mechanical alignment axes.

Medial Compartment Load Sharing and the Adduction Moment

Under physiological bipedal gait, the ground reaction force vector passes medial to the center of rotation of the knee joint, generating an external knee adduction moment (KAM). Consequently, the medial tibiofemoral compartment bears 60% to 75% of the total compressive load across the knee during stance phase. In constitutional varus alignment, this load concentration increases exponentially. Progressive cartilage erosion and subchondral bone loss further shift the mechanical axis medially, establishing a mechanical cycle that accelerates compartmental attrition while the lateral compartment remains unloaded and anatomically pristine.

Cruciate Ligament Integrity and Anteromedial Phenotype

The anterior cruciate ligament (ACL) is the primary passive restraint against anterior tibial translation and internal tibial rotation. In classic anteromedial osteoarthritis (AMOA), cartilage loss is confined to the anterior and middle thirds of the medial tibial plateau and femoral condyle, with the posterior margin of the plateau maintaining normal full-thickness articular cartilage. This pathognomonic pattern requires an intact, functionally competent ACL. When the ACL is ruptured or chronically attenuated, the contact zone shifts posteriorly across the tibia, producing posteromedial wear, subluxation, and progressive lateral/patellofemoral degeneration that invalidates unicompartmental resurfacing.

Patellofemoral Mechanics and Facet Cartilage Integrity

The patellofemoral articulation experiences forces ranging from 0.5 times body weight during level walking to over 3.5 times body weight during stair descent and deep squatting. While historical guidelines considered any patellofemoral cartilage degeneration an absolute contraindication to UKA, modern prospective analyses differentiate between asymptomatic medial/central facet wear and symptomatic lateral facet bone-on-bone disease with grooving or patellar maltracking. Medial facet changes frequently represent non-progressive degenerative remodeling that does not compromise unicompartmental longevity.

3. Clinical Case Scenario: The Young, Active Gonarthrosis Patient

The presentation of an active 56-year-old male with symptomatic unilateral knee pain illustrates the decision-making dilemmas encountered in modern adult reconstruction.

Patient Clinical Profile and Functional Demands

The patient presents with progressive, activity-related medial joint-line pain of 2 years’ duration, exacerbated by running, heavy labor, and prolonged standing. Mechanical symptoms include localized aching and startup stiffness, without true mechanical locking or instability. Conservative interventions—including physical therapy, unloader bracing, oral nonsteroidal anti-inflammatory drugs (NSAIDs), and intra-articular corticosteroid and hyaluronic acid injections—have provided diminishing temporary relief. The patient expresses a strong desire to maintain an active lifestyle, participate in recreational athletics, and avoid the functional limitations commonly perceived with conventional joint arthroplasty.

Physical Examination Benchmarks

Clinical evaluation demonstrates a mild varus alignment that corrects completely upon passive valgus stress testing with the knee in 20° of flexion, confirming absence of fixed collateral contracture. Range of motion spans 0° to 135° without flexion contracture. Palpation reveals point tenderness localized to the medial joint line; the lateral joint line, patellar facets, and pes anserine bursa exhibit zero tenderness. Stability testing demonstrates a firm endpoint on Lachman and anterior drawer maneuvers, intact posterior drawer, and stable collateral ligaments in full extension and 30° of flexion. The patella tracks congruently in the trochlear groove without crepitus or apprehension.

The Core Surgical Dilemma

In this clinical demographic, the reconstructive surgeon faces three divergent philosophical pathways: biological joint realignment (high tibial osteotomy), focal unicompartmental resurfacing (medial unicompartmental knee arthroplasty), or definitive total joint replacement (total knee arthroplasty). Balancing surgical morbidity, implant longevity, athletic expectations, and future revision complexity forms the crux of the treatment algorithm.

4. Diagnostic Workup and Algorithmic Radiographic Evaluation

Accurate clinical stratification relies upon a structured radiographic series designed to isolate compartmental wear patterns and quantify constitutional versus intra-articular deformity.

Full-Length Standing Teleoroentgenograms

Bilateral weight-bearing long-leg radiographs extending from the hip centers to the ankle mortise are mandatory. These views allow determination of the Mechanical Axis Deviation (MAD), the Hip-Knee-Ankle (HKA) angle, the Mechanical Lateral Distal Femoral Angle (mLDFA), and the Mechanical Medial Proximal Tibial Angle (mMPTA). In constitutional varus, the mMPTA is typically < 85°, indicating that the primary osseous deformity resides in the proximal tibia. Assessing whether the varus deformity is intra-articular (due to cartilage loss) or extra-articular (tibial bowing) dictates whether osteotomy or compartmental resurfacing is anatomically viable.

Rosenberg 45° Flexion Weight-Bearing PA Projection

Conventional full-extension AP radiographs consistently underestimate early-to-moderate cartilage loss. The 45° flexion posteroanterior (Rosenberg) view profiles the posterior weight-bearing condyles where dynamic contact occurs during ambulatory loading. Unmasking full-thickness cartilage loss and subchondral sclerosis on the Rosenberg projection confirms end-stage compartmental disease, while preserving a wide lateral joint space without reciprocal marginal osteophytes validates disease isolation.

Multi-Angle Merchant / Sunrise Patellofemoral Series

Axial views obtained at 30°, 60°, and 90° of flexion evaluate patellofemoral congruency, trochlear dysplasia, and facet-specific joint space loss. Severe lateral facet bone loss, lateral subluxation, or trochlear grooving represents a contraindication to isolated medial UKA. Conversely, mild medial facet joint space narrowing with preserved lateral trochlear cartilage is well tolerated and does not predict early unicompartmental failure.

Role of Magnetic Resonance Imaging (MRI)

Routine MRI is not indicated when weight-bearing radiographs demonstrate classic bone-on-bone anteromedial osteoarthritis with preserved lateral cartilage. However, in ambiguous clinical cases, MRI provides definitive assessment of ACL structural continuity, lateral meniscus integrity, and subchondral bone marrow edema patterns, ruling out occult avascular necrosis or spontaneous osteonecrosis of the knee (SONK).

5. Clinical Management Paradigms: HTO vs UKA vs TKA

Each surgical modality offers distinct biomechanical profiles, clinical tradeoffs, and rehabilitation trajectories.

High Tibial Osteotomy (HTO): Biological Realignment

High tibial osteotomy—executed via medial opening-wedge or lateral closing-wedge techniques—alters lower extremity alignment by transferring mechanical load from the diseased medial compartment to the preserved lateral compartment. HTO retains the patient’s native articular cartilage, completely preserves cruciate ligaments, and places no restrictions on high-impact athletic pursuits or heavy manual labor. However, HTO requires osseous healing (6 to 12 weeks of protected weight-bearing), carries risks of nonunion, hardware irritation, and neurovascular injury (peroneal nerve with lateral closing wedge), and alters proximal tibial anatomy (patella baja, joint line obliquity), which can increase the surgical complexity of future conversion to TKA.

Unicompartmental Knee Arthroplasty (UKA): Compartmental Resurfacing

Unicompartmental arthroplasty replaces only the damaged medial femoral condyle and tibial plateau using prosthetic components while preserving the lateral compartment, patellofemoral joint, and both cruciate ligaments. Because native kinematics, proprioception, and joint stability are retained, UKA provides superior postoperative knee flexion (averaging 10° to 15° more than TKA), faster recovery, reduced perioperative blood loss, and a markedly lower incidence of serious systemic complications (venous thromboembolism, myocardial infarction, periprosthetic infection). The primary limitation of UKA is a higher revision rate in national joint registries (roughly 2 to 3 times that of TKA), driven largely by a lower threshold for revision among non-originating surgeons, disease progression in unreplaced compartments, and aseptic loosening.

Total Knee Arthroplasty (TKA): Tri-Compartmental Replacement

Total knee arthroplasty provides definitive, highly durable resurfacing of all three compartments, yielding 15- to 20-year implant survivorship rates exceeding 90% across multicenter registry series. However, sacrificing the anterior cruciate ligament alters sagittal kinematics, produces paradoxical anterior femoral translation during flexion, and leaves approximately 15% to 20% of patients with residual stiffness, anterior knee pain, or subjective dissatisfaction (“unforgotten joint”). In a 56-year-old active individual, primary TKA also exposes the patient to the substantial clinical burden of revision surgery in later decades.

6. Indications, Patient Selection, and Contraindications

Successful execution of unicompartmental arthroplasty demands rigorous adherence to validated anatomical and functional selection criteria.

Modern Expanded Selection Criteria for UKA

• Isolated Compartmental Disease: Full-thickness articular cartilage loss (bone-on-bone) confined strictly to the medial or lateral tibiofemoral compartment.
• Functionally Intact Cruciate Ligaments: Structurally competent ACL without anterior instability or posterior tibial wear.
• Correctable Coronal Deformity: Varus deformity passively correctable to neutral without fixed contracture; intraoperative alignment must not be forced into valgus.
• Preserved Range of Motion: Minimum preoperative flexion of ≥ 90° with a flexion contracture of < 10°.
• Preserved Lateral Compartment: Full-thickness articular cartilage and intact meniscus in the opposing compartment.

Contraindications to Unicompartmental Arthroplasty

• Absolute Contraindications: Inflammatory arthropathy (rheumatoid arthritis, psoriatic arthritis), active septic arthritis, ACL deficiency with secondary posterior wear, fixed varus deformity exceeding 15°, flexion contracture > 15°, or full-thickness cartilage loss with grooving on the lateral patellar facet and lateral femoral condyle.
• Historical Misconceptions (Refuted Relative Contraindications): Patient age 30 kg/m²), high physical activity demand, and asymptomatic chondromalacia of the patella or medial trochlea are no longer considered contraindications when anatomical criteria are met.

7. Decision-Making Matrix: Surgical Options for Isolated Medial Gonarthrosis

The following comparative matrix synthesizes clinical characteristics, biomechanical considerations, and outcome benchmarks across surgical interventions for isolated medial compartment osteoarthritis.

8. Operative Principles: Technical Nuances of Partial Knee Arthroplasty

Achieving durable outcomes in medial unicompartmental arthroplasty requires precise component sizing, conservative bone resection, and strict avoidance of overcorrection.

Conservative Tibial and Femoral Resection

The tibial cut must be minimal, removing only enough bone to accommodate the prosthetic baseplate and bearing (typically 2 to 4 mm below the deepest point of the medial defect). Excessive resection enters softer cancellous bone, dramatically escalating the risk of tibial component subsidence and periprosthetic plateau fracture. The sagittal tibial slope must replicate native anatomy (typically 5° to 7° posterior slope); flattening the slope tightens the flexion gap and restricts deep flexion, while excessive slope tensions the ACL and induces anterior translation.

The Undercorrection Principle: Avoiding Valgus Transfer

Unlike total knee arthroplasty, where the mechanical axis is typically straightened to neutral (180°), unicompartmental arthroplasty must never overcorrect a varus knee into valgus. Correcting beyond the pre-morbid constitutional varus shifts the mechanical weight-bearing axis into the virgin lateral compartment, precipitating rapid articular cartilage breakdown and early failure. The intraoperative target is slight undercorrection, leaving 2° to 4° of residual mechanical varus while restoring the native joint line height.

Gap Balancing and Bearing Security

Rectangular, balanced gaps in 0° of extension and 90° of flexion are essential. In mobile-bearing systems, gap asymmetry or bearing overhang leads to bearing spin-out or dislocation. In fixed-bearing systems, tightness in extension produces polyethylene edge loading, whereas laxity in flexion generates sagittal instability and recurrent synovitis. Ligament releases (such as releasing the deep or superficial medial collateral ligament) are strictly contraindicated; gap balancing must be achieved exclusively through bone resection adjustments and component positioning.

9. Functional Outcomes, Kinematics, and Quality of Life

Clinical investigations and kinematic studies demonstrate clear physiological distinctions between joint-preserving procedures and total joint replacement.

Kinematics and the “Forgotten Knee”

Fluoroscopic and gait laboratory analyses demonstrate that knees treated with unicompartmental arthroplasty replicate normal femoral rollback, physiological external rotation during flexion, and native screw-home mechanics. Because the ACL, PCL, and mechanoreceptors within the joint capsule remain intact, patients perceive the joint as natural, yielding significantly higher Forgotten Joint Scores (FJS-12) and Oxford Knee Scores (OKS) compared with matched TKA cohorts. Active patients achieve earlier return to recreational sports, cycling, swimming, and golf.

Surgeon Volume and the Registry Revision Disparity

National joint registry data from the UK, Australia, and New Zealand demonstrate a persistent disparity: UKA has an overall higher revision rate than TKA at 10 years (approximately 10% to 15% vs 5%). However, granular registry stratification reveals this disparity is heavily driven by surgeon volume. Surgeons performing UKA as a high-usage procedure (> 20% to 30% of their total knee arthroplasty volume, or > 30 cases annually) achieve implant survivorship exceeding 90% at 10 years, matching contemporary TKA benchmarks while providing superior patient satisfaction.

10. Failure Modes and Complications

Understanding specific failure mechanisms guides surgical vigilance and streamlines revision planning.

Early Complications (0 to 6 Weeks)

• Tibial Plateau Fracture: Results from aggressive vertical sagittal cuts exceeding the posterior tibial cortex, microfractures during keel/peg preparation, or deep bone resections in osteopenic bone. Managed with open reduction and internal fixation or conversion to stemmed TKA.
• Bearing Dislocation (Mobile-Bearing Designs): Occurs due to flexion-extension gap mismatch, trapped posterior osteophytes, or ligamentous laxity in deep flexion. Requires open reduction, bearing exchange, or component realignment.
• Acute Periprosthetic Joint Infection (PJI): Low incidence (< 0.5%), substantially lower than primary TKA. Treated with debridement, antibiotics, and implant retention (DAIR) or staged revision.

Late Complications (> 6 Weeks)

• Disease Progression in Unreplaced Compartments: The leading indication for revision, occurring primarily in the lateral tibiofemoral or patellofemoral joint. Often precipitated by initial overcorrection into valgus or unappreciated preoperative lateral wear.
• Aseptic Loosening: Most commonly involves the tibial component due to cement debonding, poor bone interdigitation, or excessive load concentration from malalignment.
• Secondary Cruciate Failure: Late ACL rupture destabilizes the kinematics of unicompartmental implants, leading to rapid tibial loosening or posterior wear.

Conversion of UKA to TKA: Surgical Principles

When UKA fails, revision to TKA typically results in outcomes comparable to primary TKA, provided that the initial UKA was conservative. In the majority of revisions, standard primary TKA implants or minimal augments (5 mm medial tibial block or offset stem) suffice. Care must be taken during explantation to avoid uncontained medial tibial bone loss, preserve collateral ligament insertions, and re-establish the correct joint line height.

11. Surgical Pearls and Avoidable Pitfalls

Clinical experience dictates key intraoperative maneuvers to ensure technical precision and avoid catastrophic failure.

Technical Pearls

• Sagittal Cut Alignment: Orient the sagittal tibial cut slightly lateral to the apex of the medial tibial spine, pointed toward the anterior superior iliac spine (ASIS), ensuring the blade remains perpendicular to the mechanical coronal axis.
• Posterior Osteophyte Excision: Meticulously debride all posterior femoral and tibial osteophytes; residual posterior spurs impinge against the polyethylene bearing in deep flexion, precipitating bearing spin-out or limited flexion.
• Joint Line Restoration Check: Reference the thickness of the resected tibial bone wafer plus cartilage against the combined implant thickness; never raise or lower the native joint line by more than 2 mm.

Avoidable Pitfalls

• The Valgus Overcorrection Trap: Avoid attempting to create a perfectly straight leg; leaving the knee in 2° to 4° of constitutional varus protects the lateral compartment from accelerated degeneration.
• Violating the Posterior Cortex: Never allow reciprocating or oscillating saw blades to plunge beyond the posterior tibial cortex, which risks devastating popliteal neurovascular injury and cortical fracture.
• Collateral Ligament Release: Never release the medial collateral ligament (MCL) to balance a tight medial compartment; if the gap is tight, recut the tibia or reduce polyethylene thickness.

12. Contemporary Controversies in Adult Reconstruction

Current debates focus on implant design philosophy, robotic technology integration, and multi-compartment partial replacement.

Mobile-Bearing vs Fixed-Bearing Designs

Mobile-bearing UKA utilizes a fully congruent, unconstrained polyethylene insert that glides freely on a polished cobalt-chromium tibial tray, minimizing contact stress and theoretical polyethylene wear. However, mobile bearings introduce the unique complication of bearing dislocation and demand absolute precision in gap balancing. Fixed-bearing designs eliminate dislocation risk, tolerate minor gap asymmetries more forgivingly, and are applicable to both medial and lateral unicompartmental arthritis, with long-term clinical survivorship demonstrating comparable results between designs in experienced hands.

Robotic-Assisted and Navigated UKA

Semi-autonomous robotic arms and imageless navigation platforms provide real-time stereotactic haptic feedback, tightening implant positioning accuracy and reducing alignment outliers within 1 mm and 1°. While clinical trials demonstrate superior early radiological precision and modest improvements in early PROMs, high capital acquisition costs and extended operative duration remain subjects of ongoing cost-effectiveness debates.

Bicompartmental Arthroplasty (Medial UKA + PFA) vs Primary TKA

In patients presenting with concurrent medial tibiofemoral and patellofemoral osteoarthritis, combined unicompartmental resurfacing (bicompartmental arthroplasty) offers a joint-sparing alternative that retains cruciate ligaments. While technically demanding and associated with higher early revision rates than isolated UKA, modular bicompartmental arthroplasty provides superior functional kinematics and higher satisfaction than conventional TKA in meticulously selected active cohorts.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Chen X, Li X, Zhu Z et al. Effects of progressive resistance training for early postoperative fast-track total hip or knee arthroplasty: A systematic review and meta-analysis. Asian J Surg. 2021. doi:10.1016/j.asjsur.2021.02.007 [Level I: Systematic Review / Meta-Analysis]
• Zhang Q, Chen Y, Li Y et al. Enhanced recovery after surgery in patients after hip and knee arthroplasty: a systematic review and meta-analysis. Postgrad Med J. 2024. doi:10.1093/postmj/qgad125 [Level I: Systematic Review / Meta-Analysis]
• Zhang B, Qian H, Wu H et al. Unicompartmental knee arthroplasty versus high tibial osteotomy for medial knee osteoarthritis: A systematic review and meta-analysis. J Orthop Surg (Hong Kong). 2023. doi:10.1177/10225536231162829 [Level I: Systematic Review / Meta-Analysis]
• Weiya Zhang, Roland W. Moskowitz, G. Nuki et al. OARSI recommendations for the management of hip and knee osteoarthritis, Part II: OARSI evidence-based, expert consensus guidelines. Osteoarthritis and Cartilage. 2008. doi:10.1016/j.joca.2007.12.013 [Level V (Expert Conceptual Review): Seminal Conceptual / Observational Study]
• J. Bruce Moseley, Kimberly J. O’Malley, Nancy J. Petersen et al. A Controlled Trial of Arthroscopic Surgery for Osteoarthritis of the Knee. New England Journal of Medicine. 2002. doi:10.1056/nejmoa013259 [Level V (Expert Conceptual Review): Seminal Conceptual / Observational Study]

15. Master Class Pro-Tip

Avoiding the Overcorrection Trap in Medial Unicompartmental Knee Arthroplasty: The single greatest technical error in medial UKA is over-resection or over-stuffing the medial compartment into valgus alignment. In a native varus knee with medial bone-on-bone osteoarthritis, the constitutional mechanical axis was varus prior to joint disease. Attempting to align the mechanical axis through the center of the knee shifts load into the intact lateral compartment, causing rapid articular cartilage breakdown and early failure. The intraoperative goal is strictly to restore the pre-morbid joint line height and correct the intra-articular deformity while leaving the constitutional extra-articular varus undisturbed (leaving 2° to 4° of residual varus). Always evaluate the flexion and extension gaps with the trial components seated, ensuring that the lateral compartment does not open more than 1 to 2 mm under gentle valgus stress, and that the prosthetic joint does not capture the bearing tightly in extension.

Master Class Surgical Pearl: Compartmental Balance and Mechanical Axis Stewardship