1Patella Fractures & Extensor Mechanism Injuries Lisa K. Cannada, MDRevised: October 2008; May 2011
2Anatomy Largest sesamoid bone Thick articular cartilage proximally Articular surface divided into medial and lateral facets by longitudinal ridgeDistal pole nonarticularThe patella is the largest sesamoid bone in the body and lies within the fascia and fibers of the quadriceps tendon. The upper ¾ is covered with articular cartilage. The articular surface of the patella is divided into medial and lateral facets, which articulate with the anterior trochlea. As you can see from the diagram, the lateral facet is the largest. A vertical ridge near the medial facet defines the odd facet. Transverse ridges are present which further define the facets.
3Anatomy Patellar Retinaculum Blood Supply Longitudinal tendinous fibersPatellofemoral ligamentsBlood SupplyPrimarily derived from geniculate arteriesThe patella in invested in a strong soft tissue envelope formed by the joining of the quadriceps tendon, the iliotibial band and distal quadriceps muscles and the patella tendon. The patellar retinaculum originates from the deep fascia along with fibers of the vastus medialis and vastus lateralis. There are also contributions from the iliotibial tract and patellofemoral ligaments of the joint capsule.The blood supply consists of an extraossoeus and intraosseous vascular system. The primary blood supply is from branches of the geniculate arteries. The intraosseous blood supply enters the bone through the midportion of the patella and through distal pole vessels.
4BiomechanicsThe patella undergoes approximately 7 cm of translation from full flexion to extensionOnly 13-38% of the patellar surface is in contact with the femur throughout its range of motionThe patella is a link between the quadriceps tendon and patella tendon and is subject to significant forces. The patella increases the leverage of the quadriceps muscle and elevates the extensor mechanism away from the axis of rotation of the knee joint. The area of contact between the patella and distal femur varies according to the position of the knee.
5Biomechanics The patella increases the moment arm about the knee Contributes up to 30% improvement in lever armPatella withstands compressive forces greater than 7X body weight with squattingThe patella improves the efficiency of the extensor mechanism by elevating the quadriceps away from the axis of rotation about the knee joint. The patella increases the leverage or the quadriceps allowing it to act over a greater angle.There are significant forces generated across the patellofemoral joint with activities of daily living. Normal activities can generate up to three times the body weight across the patellofemoral joint. With squatting and stair climbing, there may be forces up to seven times the body weight generated!
6Biomechanics 2 X Torque: Extend final 15° Than to extend from a fully flexed position to 15 degrees of flexionAs mentioned, the amount of contact between the patella and trochlea varies depending upon position of the knee. With the knee fully extended, the inferior portion of the patella is in contact with the femur. With the knee flexed to 135 degrees, the patella is in the intercondylar notch. Twice as much torque is needed to extend the knee the final 15 degrees than to extend from a fully flexed position from to 15 degrees of flexion.
7Physical ExaminationPain, swelling, contusions, lacerations and/or abrasions at the site of injuryCan determine timing of operative interventionPalpable defectAssessment of ability to extend the kneeCannot perform a straight leg raise with no extensor lagOne must complete a thorough history and physical examination of the patient. There may be pain, swelling and decreased strength. The defect may be palpable. The skin should be examined closely in those injuries sustained from direct trauma to evaluate for the presence of an open injury. A saline load test may be used to assist with this diagnosis.The extensor mechanism is evaluated by the ability to extend the knee against gravity or to maintain the knee in full extension versus gravity.
8Radiographic Evaluation AP & LateralNote patella height (baja or alta)Note fracture patternArticular step-off, diastasisMarginal impactionSpecial viewsAxial or sunriseCT ScanOccult FracturesComplex or Marginal Impaction FracturesRadiographic evaluation of patella fractures includes AP, lateral and sunrise views. Comparison views of the unaffected limb may be of value to further define the bony anatomy. On the lateral view, one should evaluate the position of the patella. A low riding patella (patella baja) may indicate a quadriceps tendon rupture, while a high riding patella (patella alta) may indicate a patella tendon rupture. The Insall method method is used for assessment of patella position. In this method, the patella length is measured and compared in a ratio to length of the patella tendon. Normally, the ratio is 1. A ratio of 0.8 or less suggests a patella tendon rupture.The sunrise view may be helpful to further delineate fracture displacement. This view is helpful in the diagnosis of patellofemoral disorders and osteochondral defects.CT scans may be useful in periarticular injuries, evaluation of alignment, detection of occult fractures and analysis of fracture healing.
9Radiographic Evaluation Bipartite Patella:Don’t get fooled!Obtain bilateral viewsOften superolateral corner(Saupe Classification, 1923)Accessory ossification centerOccurs 1-2% of patientsIn the evaluation of bipartite patella, obtain bilateral views. This accessory ossification center involves the superolateral corner.
10Etiology Direct trauma Indirect trauma Direct blow to flexed knee (dashboard)Increasing cases with penetrating traumaComminution & articular marginal impactionIndirect traumaFlexion force directed through the extensor mechanism against a contracted quadricepsSimple, transverse fractureAs mentioned, there are two main mechanisms of patella fractures: direct and indirect. Direct trauma often involves a higher energy mechanism and may be accompanied by additional injuries. There may be more damage to the articular cartilage which ultimately may affect the outcome.
11Classification Allows guidance with treatment Types Transverse MarginalVerticalComminutedOsteochondralAvulsion (not pictured)Classification systems are ideally designed to allow communication between physicians, guide treatment and predict outcomes. For the patella, there is no universally accepted classification systems other than the OTA system. Descriptive terms may be used to classify patella fractures and an example is demonstrated on the slide.Tip: Vertical fractures may not result in disruption of extensor mechanism
13Nonoperative Treatment Indicated for minimally or nondisplaced fractures< 2mm of articular step-off & < 3mm of diastasis with an intact extensor mechanism (extensor retinaculum)If difficulty assessing, consider intra-articular injection of local anesthetic to better assess ability to extendConsider for minimally displaced fractures in low demand patients (evaluate comorbidities & function)Patients with a extensive medical comorbiditiesTreatment of patella fractures is bases on the fracture type and physical examination. The ultimate goals are to preserve and/or restore extensor mechanism function and reduce complications of this articular fracture. Nonoperative treatment is indicated for nondisplaced fractures with an intact extensor mechanism, fractures with less than 2mm of articular step off and less than 3mm of diastasis. Nonoperative treatment may also be indicated for elderly patients or those patient with underlying medical co morbidities which preclude surgery.
14Nonoperative Treatment Long leg cylinder cast for 4-6 weeksMay consider a knee immobilizer or hinged knee brace for the elderly/low demandImmediate weight-bearing as toleratedRehabilitation includes range of motion exercises with gradual quadriceps strengtheningProtect eccentric contraction 3 monthsNonoperative treatment consists of a long leg cylinder cast for 4-6 weeks with weight bearing as tolerated. An alternative is a hinged knee brace or knee immobilizer. Rehabilitation should include ROM exercises once the cast is discontinued and quadriceps strengthening.
15Operative Treatment Goals Preoperative Setup Approach Preserve extensor functionRestore articular congruencyPreoperative SetupTourniquet (debatable)Prior to inflation, gently flex the kneeApproachLongitudinal midline incision recommendedTransverse approach alternative (dotted lines) – potentially higher risk wound problems, can limit initiation of ROMConsider future surgeries!Operative treatment is indicated for displaced fractures and disruption of the extensor mechanism. There are many options which will be discussed. Planning is essential. The patient is positioned supine on the table. A well padded tourniquet should be applied to the proximal thigh. The knee should be flexed to lengthen the quadriceps and bring the proximal fragment distal before the tourniquets is inflated. This prevents entrapment of the tissues.Approaches to the patella include a transverse incision over the mid-patella. Most surgeons now recommend a midline incision. This is useful if further reconstructive procedures are necessary in the future.
18Operative Techniques K-wires w/ tension band wiring (TBW) Lag-screw fixationCannulated lag-screw with TBW (tension band screw – TBS)Partial patellectomyTotal PatellectomyOK to change title??
19Tension Band Wiring Transverse, non-comminuted fractures Reduce and clamp, then place two parallel 1.6mm K- wires placed perpendicular to the fracture18 gauge wire passed behind proximally and distallyDouble Figure-8 wire for equal compressionModified tension band wiring is good for transverse patella fractures. After exposure of the fracture, the fracture is cleared of clots and debris. The articular surface is inspected. The fracture is reduced with clamps and evaluated for any malreduction. Two parallel K-wires may be placed through a retrograde or antegrade manner. A 14 or 16 gauge angiocathether is passed behind the quadriceps and patella tendon adjacent to the bone. An 18 gauge wire is passed through the catheters to encircle the patella. The wire is then tightened.
20Tension Band WiringWire converts anterior distractive forces to compressive forces at the articular surfaceTwo twists are placed on opposite sides of the wireTighten simultaneously to achieve symmetric tensionRetinacular InjuryKeep open until the endWindow to assess articular reductionRepair the retinacular injury lastWith a tension band technique, the purpose is to convert distractive forces to compressive forces. Once the reduction of the fracture is adequate, a wire twister should be used to tension the wire. The medial and lateral limbs of the wires are sequentially tightened to apply the tension symmetrically. Once should be cautious about over tightening the wires, which may lead to loss of reduction or compression of comminuted fracture fragments. The ends of the wires are cut and turned over the tension band loop with the ends buried in bone.Once the fracture is adequately reduced, the retinaculum should be inspected for tears and repaired.
21Lag-Screw FixationIndicated for stabilization of comminuted fragments in conjunction w/ cerclage wires if necessaryMay also be used as an alternative/adjunct to TBW for transverse or vertical fracturesLag screw fixation may be used in conjunction with other techniques or alone. It may be particularly useful in a fracture with multiple pieces to help reduce minor fragments into major fragments or in proximal or distal pole fractures.
24Lag-Screw FixationContraindicated for extensive comminution and osteopenic boneSmall secondary fractures may be stabilized with 2.0mm, 2.7mm or 3.5mm cortical screwsReduce out of plane fragments to main fragments superiorly and inferiorlyTransverse or vertical fractures require 3.5mm, 4.0mm, or 4.5mm cortical screwsRetrograde insertion of screws may be technically easierLag screw fixation is contraindicated in fractures with extensive comminution or osteopenic bone. If stabilizing minor fragments into major fragments, the smaller fragments may be secured with 2.7 or 3.5 mm screws. Major fragments of transverse or vertical fractures should be fixed with 3.5 or 4.5 mm screws.
25Cannulated Lag-Screw With Tension Band (TBS) Partially threaded cannulated screws (4.0mm)Wire through screws and across anterior patella in figure of eight tension bandMake sure tip of screw remains buried in bone so it will not compromise wireA technique I prefer for fixation of transverse fractures is cannulated lag screws with tension band. The screws may be inserted antegrade or retrograde depending on fracture location. 18 gauge wire may be used for the tension band as previously described. An alternative, especially in thin patients or those with thin skin, is the use of cannulated screws and figure of eight tension band with a #5 Ethibond suture. A study in Injury (Vol 1:1-6, 2000) found the quality of fixation for braided polyester suture was comparable to that of stainless steel wire for patella fractures.
26Cannulated Lag-Screw With Tension Band More stable constructScrews and tension band wire combination eliminates both possible separation seen at the fracture site with K wire/TBW and screw failure due to excessive three point bendingScrews plus the tension band technique is the most stable construct for fixation of transverse fracture patterns in biomechanical studies. The addition of screws to the tension band technique reduces minimizes fracture separation by providing compression through the range of motion and minimizing screw failure due to excessive three point bending.
27Suture vs. Wire Tension Band Gosal et al Injury 2001Wire v. #5 Ethibond37 patientsReoperation 38% wire group vs. 6%Infection 3 pts wire group vs. 0Patel et al, Injury 2000McGreal et al, J Med Eng Tech, 1999Cadaveric modelsQuality and stability of fixation comparable to wireConclude suture an acceptable alternative
28Partial PatellectomyIndicated for fractures involving extensive comminution not amenable to fixationLarger fragments repaired with screws to preserve maximum cartilageSmaller fragments excisedUsually involving the distal poleIf there are fractures with severe comminution not amenable to fixation, a partial patellectomy may be indicated. If there are cases with significant comminution of the inferior pole, resection with repair of the patella tendon is done.
29Partial PatellectomyTendon is attached to fragment with nonabsorbable suture passed through drill holes in the fragmentDrill holes should be near the articular surface to prevent tilting of the patellaLoad sharing wire passed through drill holes in the tibial tubercle and patella may be used to protect the repair and facilitate early range of motionIt is important not to disturb the biomechanics of the patellofemoral joint and maintain the proper alignment of the extensor mechanism. Visualization of the articular surface may prevent malreduction. Watch for alterations of patellar tilt!Due to the significant forces across the extensor mechanism, it is recommended to evaluate the stability of the repair by flexing to 90 degrees. It may be necessary to reinforce with wire, Mersilene tape or a fascial graft. The reinforcement should be placed with the knee flexed to minimize contractures post-operatively.Results in the literature (Bostman, Nummi, Mischra) demonstrated near normal outcomes when large fragments and the articular surface were maintained.
30Total PatellectomyIndicated for displaced, comminuted fractures not amenable to reconstructionBone fragments sharply dissectedDefect may be repaired through a variety of techniquesUsually results in extensor lag (30°) and loss of strength (30%) – H Kaufer, JBJSTotal patellectomy should be reserved for a salvage procedure due to failed previous repairs or infection. I do not recommend this as a primary procedure.During the approach, full thickness flaps should be developed. Bone fragments should be sharply excised. The resulting defect can be repaired through a variety of techniques and is the most important part of the procedure.There is alteration in the patella-femoral biomechanics post operatively. The quadriceps is lengthened, which results in an extensor lag and quadriceps weakness. It is recommended to perform an imbrication to shorten the mechanism.The results in the literature are less than optimal with significant loss of strength. Difficulty with ADL’s and many patients with a fair to poor result.
31Postoperative Management Immobilization with knee brace, WBAT in extensionEarly range of motionBased on intraoperative assessment of repair & bone qualityActive flexion with passive extensionQuadriceps strengtheningBegin when there is radiographic evidence of healing, usually around 6 weeksModify depending upon fracture, osteoporosis, comorbidities, tenuous fixation and/or wounds at riskThe surgeon should evaluate the stability of the fracture intra-operatively to plan the post-operative regimen. Immobilization with a hinged knee brac permits appropriate increases in ROM as rehabilitation proceeds. The patients without other lower extremity injuries are allowed WBAT. With a stable fixation, early ROM exercises may be initiated. Active and gentle passive motion may facilitate the rehabilitation. ROM exercises should be delayed until there is appropriate soft tissue healing.Initially strengthening should consist of quadriceps isometric exercises and as the fracture demonstrates evidence of healing, resistive exercise may be started.
32Complications Knee Stiffness Infection Loss of Fixation Osteoarthritis Most common complicationInfectionRare, depends on soft tissue compromiseLoss of FixationHardware failure in up to 20% of casesOsteoarthritisMay result from articular damage or incongruityNonunion < 1% with surgical repairPainful hardwareRemoval required in approximately 15%
36Extensor Tendon Ruptures Patients are typically males in their 30’s or 40’sPatellar < 40 yoQuadriceps > 40 yoMechanismFallSports “The weekend warrior”MVATendonopathies, Steroids, Renal DialysisPatella and quadriceps tendon ruptures are thought to be uncommon injuries. Patients are typically males in their thirties and forties. There is a trend for patella tendon ruptures in patients under 40 years old, while the same mechanism usually results in quadriceps tendon ruptures in patients over 40. The “weekend warrior” athlete is usually the patient I see with these injuries.Other mechanisms include falls and MVC’s.
37Quadriceps Tendon Rupture Typically occurs in patients > 40 years oldUsually 0-2 cm above the superior poleLevel often associated with ageRupture occurs at the bone-tendon junction in majority of patients > 40 years oldRupture occurs at midsubstance in majority of patients < 40 years old
38Quadriceps Tendon Ruptures Risk FactorsChronic tendonitisAnabolic steroid useLocal steroid injectionInflammatory arthropathyChronic renal failureSystemic diseaseThere are several risk factors described for quadriceps (and patella) tendon ruptures. These include steroid use (systemic or local), chronic tendonitis, inflammatory arthritis and chronic renal failure. Chronic systemic disease such as lupus, rheumatoid arthritis and diabetes are also risk factors, especially for quadriceps tendon ruptures.
39HistorySensation of a sudden pop while stressing the extensor mechanism (eccentric load)Pain at the site of injuryInability to extend the kneeDifficulty weight-bearing
40Physical Exam Effusion Tenderness at the upper pole Palpable defect above superior poleLoss of extensionWith partial tears, extension will be intactPhysical examination reveals an effusion, tenderness at the upper pole and you can often palpate a defect. There is loss of ability to extend the leg. The key is differentiation of the partial from complete rupture. A delay in diagnosis may occur with quadriceps tendon ruptures as there may not be radiographic abnormalities.
41Quadriceps Tendon Rupture Radiographic EvaluationX-ray- AP, Lateral, and Tangential (Sunrise, Merchant)Distal displacement of the patella (patella baja)MRIUseful when diagnosis is unclearTreatmentNonoperativePartial tears and strainsOperativeFor complete ruptures
42Operative TreatmentReapproximation of tendon to bone using nonabsorbable sutures with tears at the muscle-tendon junctionLocking stitch (Bunnel, Krakow) with No. 5 ethibond passed through vertical bone tunnelsRepair tendon close to articular surface to avoid abnormal patellar tiltingEarly primary repair of quadriceps tendon ruptures in recommended. The tendon edges are debrided and the superior pole of the patella is prepared.A locking suture is placed in the tendon and passed through vertical bone tunnels. Attention to patellar tilt is essential.
43Operative TreatmentMidsubstance tears may undergo end-to-end repair after edges are freshened and slightly overlappedMay benefit from reinforcement from distally based partial thickness quadriceps tendon turned down across the repair site (Scuderi Technique)
44TreatmentChronic tears may require a V-Y advancement of a retracted quadriceps tendon (Codivilla V-Y-plasty Technique)
45Postoperative Management Knee immobilizer, Hinged Knee Brace, or cylinder cast for 5-6 weeksImmediate weight-bearing as toleratedAt 2-3 weeks, hinged knee brace starting with 45 degrees active range of motion with degrees of progression each week
46Complications Rerupture Persistent quadriceps atrophy/weakness Loss of motionInfection
47Patellar Tendon Rupture Less common than quadriceps tendon ruptureAssociated with degenerative changes of the tendonRupture often occurs at inferior pole insertion sitePatella tendon ruptures are uncommon. They usually occur in a younger population as an isolated injury, but may occur with other traumatic injuries. The often are at the bone-tendon interface at the inferior pole of the patella. A chronic “jumper’s knee” or tendonitis may precede the rupture.
49Anatomy Patellar tendon Averages 4 mm thick but widens to 5-6 mm at the tibial tubercle insertionMerges with the medial and lateral retinaculum90% type I collagen
50Blood SupplyFat pad vessels supply posterior aspect of tendon via inferior medial and lateral geniculate arteriesRetinacular vessels supply anterior portion of tendon via the inferior medial geniculate and recurrent tibial arteriesProximal and distal insertion areas are relatively avascular and subsequently are a common site of rupture
51Biomechanics Greatest forces are at 60 degrees of flexion 3-4 times greater strain are at the insertions compared to the midsubstance prior to failureForces through the patellar tendon are 3.2 times body weight while climbing stairs
52HistoryOften a report of forceful quadriceps contraction against a flexed kneeMay experience and audible “pop”Inability to weightbear or extend the knee
53Physical Examination Palpable defect Hemarthrosis Painful passive knee flexionPartial or complete loss of active extensionHigh riding patella on radiographs (patella alta)The patient with a complete patella tendon rupture presents with a palpable defect. ROM is painful. There is a partial or complete loss of ability to extend the knee. With partial tears, one may lack full extension. To assist with physical examination, you may consider knee aspiration and injection of lidocaine to better evaluate ROM.Radiographs reveal a patella alta.
54Radiographic Evaluation AP and Lateral X-rayPatella alta seen on lateral viewPatella superior to Blumensaat’s lineUltrasonagraphyEffective means to confirm diagnosis by determining continuity of tendonOperator and reader dependantMRIEffective means to assess patellar tendon, especially if other intraarticular or soft tissue injuries are suspectedRelatively high cost
55Classification No widely accepted means of classification Can be categorized by:Location of tearProximal insertion most commonTiming between injury and surgeryMost important factor for prognosisAcute: < 2 weeksChronic: > 2 weeks
56TreatmentSurgical treatment is required for restoration of the extensor mechanismRepairs categorized as early or delayed
57Early Repair Better overall outcome Primary repair of the tendon Surgical approach is through a midline incisionIncise just lateral to tibial tubercle as skin thicker with better blood supply to decrease wound complicationsPatellar tendon rupture & retinacular tears are exposedFrayed edges and hematoma are debrided
58Early RepairWith a Bunnell or Krakow stitch, two ethibond sutures or their equivalent are used to repair the tendon to the patellaDrill holes in patella in mid-sagittal plane to prevent cut out of sutureSutures passed through three parallel, longitudinal bone tunnels and tied proximally
59Early Repair Repair retinacular tears May reinforce with wire, cable or umbilical tapeAssess repair intraoperatively with knee flexion
60Postoperative Management Maintain hinged knee brace which is gradually increased as motion increases (tailor to the patient)Immediate vs. delayed (3 weeks) weightbearing as toleratedAt 2-3 weeks, hinged knee brace starting with 45 degrees active range of motion with degrees of progression each weekImmediate isometric quadriceps exercisesAll restrictions are lifted after full range of motion and 90% of the contralateral quadriceps strength are obtained; usually at 4-6 monthsPost-opertively after extensor tendon reparis, maintain hinged knee brace which is gradually increased as motion increases (tailor to the patient)I allow immediate WBAT. Otherwise, there may be excessive forces across the repair as one attempts partial weight bearing.At 2-3 weeks, start with 45 degrees active range of motion with degrees of progression each week. Immediate isometric quadriceps exercises may be initiated. Resistive strengthening is usually delayed until the tendon repair is healed (3 months).All restrictions are lifted after full range of motion and 90% of the contralateral quadriceps strength are obtained; usually at 4-6 months
61Delayed Repair > 6 weeks from initial injury Often results in poorer outcomeQuadriceps contraction and patellar migration are encounteredAdhesions between the patella and femur may be presentOptions include hamstring and fascia lata autograft augmentation of primary repair or Achilles tendon allograft
62Postoperative Management More conservative when compared to early repairBivalved cylinder cast for 6 weeks; may start passive range of motionActive range of motion is started at 6 weeks
63Complications Knee stiffness Persistent extensor weakness Rerupture InfectionPatella baja (Insall-Salvati ratio of < 0.8)
64References Patella Fractures: New Hughes SC, Stott PM, Hearnden AJ, Ripley LG: A new and effective tension band braided polyester suture technique for transverse patellar fracture fixation. Injury 2007:38:Luna-Pizarro D, Amato D, Arellano F, Hernandez A, Lopez-Rojas P: Comparison of a technique using a new percutaneous osteosynthesis device with conventional open surgery for displaced patella fractures in a randomized controlled trial. J Orthop Trauma 2006; 20:
65References Patella Fractures: Classic Carpenter JE, Kasman R. Matthews LS: Fractures of the patella. Instr Course Lect 1994: 43:Burvant JG, Thomas KA, Alexander R, Harris MB. Evaluation of methods of internal fixation of transverse patella fractures: A biomechanical study. J Orthop Trauma 1994;8:Einola S, Aho AJ, Kallio P. Patellectomy after fracture: long term follow-up results with special reference to functional disability. Acta Orthop Scand 1976:47:
66References: Extensor Mechanism Injuries Siwek CW, Rao JP. Ruptures of the extensor mechanism of the knee joint. J Bone Joint Surg Am 1981; 63:Bhargava SP, Hynes MC, Dowell JK. Traumatic patella tendon rupture: early mobilization following surgical repair. Injury 2004;35:76-79.Konrath GA, Chen D, Lock T et al. Outcomes following repair of quadriceps tendon ruptures. J Orthop Trauma 1998;12:
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