· causes of accelerated wear
· malalignment of lower limb
· intra-articular fracture
· meniscectomy
· osteochondritis dessicans
· avascular necrosis
· ruptured ACL
· fewer complications
· higher earlier success rate
· more rapid rehabilitation
· preserves nearly normal knee kinematics
· preserves ACL, PCL, PF jt and other compartment
· better ROM
· technically difficult
· inferior results to TKR
· compromises future TKR
· age > 60
· inactive
· weight < 80 kg
· unicompartmental OA
· infection
· recent or remote
· increased activity
· esp. heavy labouring
· young age
· esp. < 50 yrs
· significant degenerative changes in ‘normal’ compartment
· mild chondromalacia accetable
· instability
· esp. ACL deficiency
· inflammatory arthritis
· includes chondrocalcinosis
· progression inevitable
· stiffness
· flexion arc < 90o
· overweight
· 70% patient satisfaction at 10 yrs
· 85% survivorship at 10 yrs
· all modern designs tricompartmental
· medial and lateral compartments
· patellofemoral joint
· really minimally constrained
· depend greatly on integrity of soft tissues
· soft tissue balancing very important
· rarely used
· very few implants fit this category
· most common type
· degree of constraint varies widely
· can be classified according to approach to posterior cruciate
Types
PCL-retaining
· least constrained
· advantages
· restores normal knee kinematics (esp. axial rotation of tibia and increased rollback of femur on tibia)
· maintenance of ligament’s proprioceptive abilities
· maintenance of load transfers by PCL
· disadvantages
· must restore joint line to prevent increased joint reaction forces and change to kinematics of knee
· contraction of PCL may contribute to flexion deformity
· may prevent adequate access to proximal tibia
PCL-sacrificing
· more constrained
· advantages
· avoids necessity to exactly restore joint line
· provides better access
· prevents flexion deformity from PCL
· disadvantages
· loss of PCL’s effect on knee kinematics
PCL-substituting
· most constrained
· uses central buildup on tibial polyethylene
· acts as cam during knee movements
· advantages
· allow exposure and ligament correction of PCL-sacrificing prosthesis
· reproduce kinematic effects of PCL
Differences
· little functional difference or survival rate
· little difference during level gait
· difference on stair-climbing
· absence of PCL causes weight-shift forward
· really constrained in one or more planes
· include
· pure hinge
· linked hinge
· nonlinked hinge
· allow flexion-extension but do not allow abduction-adduction
· some allow rotation in transverse plane
· significant strain on bone-implant interface
· rarely used
· disabling knee pain
· functional impairment
· significant arthritis on radiographs
· most commonly performed for
· OA
· RA
· elderly
· thin
· relatively inactive
· low functional demands
· no major medical illnesses
· not a candidate for HTO
· failed nonoperative treatment
· active sepsis in knee or elsewhere
· nonfunctioning extensor mechanism
· neuropathic arthropathy
· past history of osteomyelitis
· significant peripheral vascular disease
· medical condition that precludes anaesthesia or rehabilitation
· young patient
· high-demand activities
· midline skin incision
· if previous incision
1. longitudinal
· use if possible
· leave wide bridge if impossible
2. transverse
· intersect at 90o
· medial parapatellar approach
· common in
· revision surgery
· previous HTO
· patella infera
· consequences
· difficulty everting patella
· avulsion of patellar tendon
· addressed by sequential techniques
Soft tissue release
· extensive medial and lateral release from tibia
· removal of scar from medial and lateral gutters
Lateral release
· of patella
V-Y quadricepsplasty
· medial parapatellar arthrotomy extended laterally from proximal to distal
· forms inverted V
· closed later as Y
Tibial tuberosity osteotomy
· more difficult
· requires firm reattachment
· higher incidence of complications
· valgus, varus or flexion deformity leads to soft tissue contractures
· affects alignment
· soft tissue release on concave side of deformity required
· should be preceded by complete excision of osteophytes
· effectively lengthens tight structure
Varus
· strip from proximal tibia
· medial capsule
· pes anserinus
· MCL
Valgus
· strip lateral capsule from proximal tibia
· release ITB
· strip origin of LCL from femoral condyle
· divide popliteus tendon
Flexion
· judicious bone cuts
· remove posterior osteophytes
· strip posterior capsule and gastrocnemius origins from distal femur
Femur
· 7o valgus
· intramedullary guide best
· extramedullary if long stem of THR or malalignment from femoral fracture
Tibia
· perpendicular to longitudinal axis
· parallel to floor
· extramedullary guide best
· intramedullary limited by tibial diameter and bow in 30o
Femur
· slight external rotation
· esp. if patellar maltracking anticipated
Tibia
· 3o posterior tilt
· anterior bone weakest
· rotation to point to medial third of tibial tubercle
· internal rotation leads to increased Q angle
Joint line
· restore to original level as closely as possible
· from tibia
Bone resection
· more extensive than normal tibial bone resection
· to achieve level proximal tibial surface
· should not resect distal to fibula
· results in
· smaller surface area
· cortical rather than cancellous bone
Bone graft
· obtained from femoral cuts
· tailored to fit defect
· fixed with two screws
Customised implants
· metal wedges of differing sizes and shapes available
· attached to prosthesis with bone cement
· best technique controversial
· cement
· press-fit with porous ingrowth
Cemented
· is current standard
· has longest followup
· survival of 95% at 10 yrs and 90% at 15 yrs
· incomplete radiolucent lines do not correlate with results
· best results with
· correct limb alignment
· adequate coverage of cut surface of tibia
· metal backing of tibial component
· more problems with tibial fixation
· potential problems with cement
· time-dependent fatigue
· heat-induced osteonecrosis
· particulate debris with osteolysis
Uncemented
· initial results comparable
· long-term results inferior
· increased subsidence
· increased loosening
· metal fatigue
· debonding
· improved design
· stem
· screws
· controversial
· commonest complication is from PF joint
Options
Nonresurfaced
· if not resurfaced, problems with local pain
· reported incidence of 10-25%
· increased with
· inflammatory arthropathy
· poor tracking
· obvious arthritic changes
Resurfaced
· if resurfaced
· complication rate of 5-10%
· accounts for 50% of complications
· changing with newer prosthetic design
· problems with
1. mechanical failure
· of implant, implant-bone interface and patella itself
· implant failure worse with early metal-backed components
· usually due to thin polyethylene or inadequate fixation of polyethylene to metal backing
· decreased incidence with all-polyethylene components
· fixation failure problem with overly aggressive bone resection and poor patellar preparation
· patellar fracture seen with excessive bone resection and holes in patella for fixation
2. dynamic instability
· maltracking, subluxation and dislocation
· from component malalignment and inadequate soft tissue balancing
· incidence of 4%
Comparison
· studies show no difference wrt. pain or function in bilateral TKR where only 1 patella resurfaced
Indications
Resurface
· patient
· elderly
· overweight
· disease
· inflammatory (esp. RA)
· patellofemoral joint
· severe arthritic changes (eburnated bone)
· maltracking
Do not resurface
· patient
· young
· not overweight
· disease
· not inflammatory
· patellofemoral joint
· minimal arthritic changes
· normal tracking
· other pathology
· revision with difficulty achieving fixation
· previous patellar fracture
· extreme alta or baja
Technique
Patellar height
· avoid increasing overall height of patella
· increases joint reaction force
· can lead to
· early failure
· decreased ROM
· avoid tilting patella
Prosthetic placement
· medialise patella
· lateralise femoral component
· externally rotate femoral component
· do not internally rotate tibial component
Lateral release
· assess tracking before retinacular closure
· perform lateral release if patella shows tilt or subluxation
Prosthetic choice
· anatomic patella
· femoral prosthesis with deep conforming patellar groove and raised lateral flange
Patellectomy
· may lead to posterior subluxation of tibia
· should use PCL-retaining or substituting prosthesis
Advantages
· decreases polyethylene deformation and wear
· reduces stress at implant-bone and implant-cement interface
· ability to porous coat surface for uncemented design
· ability to supplement fixation with screws
· longer survival
· decreased incidence of polyethylene failure
Disadvantages
· reduces thickness of polyethylene
· provides interface for generation of wear particles
Conclusion
· strong evidence to use metal-backed designs
Advantages
· theoretical as above for
· polyethylene
· stress
· fixation
· improved with
· increased polyethylene thickness
· congruity of PF joint
Disadvantages
· wearthrough of polyethylene
· disassociation of polyethylene from metal backing
· failure of bony ingrowth
Conclusion
· all polyethylene should be used with current designs
· metal-backed may be better with future designs
· theoretical advantage of identification and control of major bleeding vessels
· total blood loss increased by tourniquet release
· no difference demonstrated wrt
· blood loss
· wound healing
· rehabilitation
· increased infection rate if drains retained > 24 hrs
· results comparable to primary TKR
· problems with
1. increased infection rate
· related to staple
2. altered patellofemoral mechanics
· relative patella infera
· lateral release often required
· increased necessity for extensor mechanism procedure to gain access
· antibiotics
· anticoagulants
· mobilise weight-bearing on day 3
· quadriceps exercises
· splint when mobilising until independent SLR
Advantages
· improves clearance of blood from joint
· reduces need for analgesia
· increases early and late flexion of knee
Disadvantages
· interferes with wound healing
· negated by
· limiting ROM to 40o for first 3 days
· then gradually increasing ROM by 10o per day to 90o
· final ROM fairly similar
· usually 110-115o
· may not be reached for 6 months
· MUA indicated if < 90o flexion at 6 weeks
· need to exclude other causes
· RSD
· infection
· compoment malposition
· average failure rate of 1% per year
· 90% survivorship at 10 yrs
· rates are
· DVT - 50-84%
· asymptomatic PE - 8-17%
· symptomatic PE - 0.5-3%
· death - 0.3%
· most commonly in calf
· most effective prophylaxis is
· warfarin
· sequential compression
· rate of 1-2%
· see other section
· includes
· marginal necrosis
· wound slough
· sinus tract formation
· dehiscence
· haematoma
· incidence is 10-15%
· prevention
· avoidance of closely parallel scars
· gentle tissue handling
· avoidance of undermining and thin skin layers
· careful closure of deep layer
· closure with knee in flexion
· treatment
· aggressive surgical debridement and closure
· may need split skin graft or flap
· most common complication
· includes
1. malalignment
· subluxation and dislocation
· articular erosion
2. patellar fracture
· stress fracture
3. component loosening
· much more common in tibia than femur
· diagnostic features
· pain on weight bearing
· complete radiolucent line > 2 mm which is increasing
· increased uptake on bone scan
· angular deformity with subsidence
· prevented by
· metal backing
· central stem
· restricted resection with preservation of firm subcortical bone with large surface area
· adequate coverage of tibial plateau
· modern cementing technique
· precise limb realignment
· treatment
· revision arthroplasty
· of polyethylene insert
· leads to
· osteolysis
· component failure
· increased with
· nonmetal backed implant
· thin polyethylene (< 6 mm)
· heat-pressed polyethylene (delamination)
· minimally conforming surfaces (point loading)
· third-body wear (esp. cement)
· malalignment of limb
· prevented by avoidance of above factors
· uncommon in metallic components
· almost always in hinged types
· polyethylene failure seen
· usually preceded by wear
· associated with above factors
· most common in supracondylar region
· may be due to
· femoral notching
· stress shielding
· osteolysis
· more common in
· osteoporosis
· revision surgery
· treatment
· traction and functional brace
· IM supracondylar nail
· plate
· revision of prosthesis with long stem
· uncommon
· typically occurs
· months after surgery
· after revision
· prior HTO
· may be treated nonoperatively if
· minimal extensor lag
· minimal functional defect
· otherwise fixed operatively
· tendon reattached with staples
· may be reinforced with wire
Arterial injury
· occurs in 0.05%
· include
1. thrombosis
· femoral or popliteal
· more common with tourniquet in atherosclerosis
2. vessel transection
· variety of presentations
· acute ischaemia
· traumatic aneurysm
· AV fistula
Nerve injury
· peroneal nerve damage
· occurs in 3%
· causes
· correction of valgus deformity
· intraoperative traction
· bandage
· haematoma
· all recover partially
· 50% recover completely
· unclear
· probably works by removal of
· cartilage debris
· crystals
· inflammatory factors
· able to treat internal derangement at same time
· other procedures contraindicated
· to postpone TKR
· effective in 50%
· more effective if
· recent onset pain
· mechanical symptoms
· radiographic changes minimal
· ineffective in
· long-standing disease
· severe degenerative changes
· aseptic loosening
· infection
· wear and breakage
· fracture
· clinically assess
· skin and subcutaneous tissue
· old incisions
· extensor mechanism
· ligaments
· ROM
· x-ray to assess
· distal and posterior femur
· tibia
· patella
· exclude using
· clinical findings
· ESR and CRP
· bone scan
· aspiration if necessary
· old incision
· soft tissue release
· may need quadricepsplasty
Removal
· careful removal of old prosthesis
· thin osteotome
· Gigli saw
· customised prosthesis
· semiconstrained
· long stem
· bone wedges
Classification
· minimal
· < 50% of condyle
· depth < 5 mm
· moderate
· 50-75% and 5-10 mm
· severe
· > 75% and > 10 mm
· massive
· rim defect
Solutions
· component translation away from defect
· for minimal defects
· increased bone resection
· for minimal or moderate defects
· cement
· used alone for minimal defects
· combined with screws for moderate defects
· bone graft
· autograft for moderate and severe defects
· allograft for massive defects
· metal wedges
· for peripheral defect
· stem
· added to above techniques
· to improve fixation
· 75% good or excellent at 5 yrs
· 33% complication rate