SURGICAL TECHNIQUES IN THE
`PERFORMANCE OF UNICOMPARTMENTAL
`ARTHROPLASTIES
`
`PETER A. KEBLISH, JR, MD
`
`The technical principles of unicompartmental knee arthroplasty (UKA) are similar to but subtly different from total
`knee arthroplasty (TKA}. Reestablishing the joint line of the diseased compartment and restoring the altered anterior
`cruciate ligament, posterior cruciate ligament, and collateral (medial and lateral) kinematics are the goals of surgery.
`When proper indications exist, normal knee function is possible. Instrumentation systems plus surgical expertise
`must provide for accurate compartment resurfacing of the femoral condyle and tibial plateau. Technical errors of
`malposition (rotational, varus-valgus, flexion-extension) and gap imbalance (depth of resection) will negatively affect
`stability, mobility, wear, and fixation with less than satisfactory clinical outcomes. Because few UKAs are performed,
`even by so-called experts, more attention to detail is required. Excellent long-term results can be appreciated when
`patient selection, prosthetic design, and surgical technique are optimal. This section addresses the key technical
`aspects of UKA that will affect clinical results.
`KEY WORDS: arthroplasty, knee prosthesis, prosthesis design
`
`Unicompartmental knee arthroplasty (UKA) provides
`an alternative to high tibial osteotomy (HTO} and total
`knee arthroplasty (TKA) for angular knee deformity, Crite~
`ria and selection factors in the literature to date have been
`coilservative.14 The procedure is us1.1ally re¢ommended for
`relatively inactive, elderly patients. An increasing number
`of patients, however, are more youthful, more active, will
`liv¢ longer, and desire to maintain. an active lifestyle,
`mcluding recreational athletics, such as tentris, skiing, and
`so on. These patients may be too young for TKA and may
`not meet the treatment criteria for HTO or newer ap(cid:173)
`proaches, such as autologous cartilage autotransplantation
`and allograft (bone, cartilage, meniscal) transplantation.5
`Improveineht in prosthetic design, materials, instrumenta(cid:173)
`tion, and surgical technique have renewed interest in UKA
`for this patient group.
`The philosophy of UKA is to realign minimal, correct(cid:173)
`able angular deformity while preserving normal kinemat(cid:173)
`ics. The procedure entails a resurfacing to reestablish the
`normal ligament environment (cruciates and collaterals)
`and the mechanical axis to the premorbid alignment,
`which is dictated by collateral ligament tension. Flexion(cid:173)
`extension balancing must be accomplished without length(cid:173)
`ening releases, subtle elevation of the joint line, overload(cid:173)
`ing the opposite compartment, overcorrection, or creating
`patellofemoral impingement.
`Patient selection remains the most important factor if
`early failures are to be avoided. All investigators have
`stressed that UKA patient selection is most important,
`
`From the Division of Orthopaedic Surgery, Lehigh Valley Hospital,
`Allentown, PA; and the Penn State University College of Medicine,
`Hershey, PA.
`Address reprint requests to Peter Keblish, MD, 1243 S. Cedar Crest
`Blvd, Suite2500,AIIentown, PA 18103.
`Copyright© 1998 by W.B. Saunders Company
`1 048-6666/98/0803-0002$08.00/0
`
`134
`
`includingproper diagnosis, age, activity level, weight, and
`appropriate imaging studies (magnetic resonance imaging,
`computed tomography scans) to confirm noninflammatory
`single compartment disease. Most agree that the patient
`should have a correctable deformity, an intact anterior
`cruciate ligament (ACL), no or minimal opposite compart(cid:173)
`ment, or no patellofemoral involvement (Fig 1). The pa(cid:173)
`tient should be well motivated with a good understanding
`of the philosophy of the procedure. Many patients have
`had previous arthroscopic surgery with well-documented
`compartment pathology and overall joint assessment. How(cid:173)
`ever, conversion to TKA at surgery, if indicated, must be
`agreed upon by the patient because more extensive disease
`may be present than had been anticipated.
`Prosthetic design, the second major factor in successful
`UKA, must allow for unconstrained motion without me(cid:173)
`chanical (translational or rotational) blocks.6 Designs that
`have attempted to introduce increased stability without
`allowing for mobility have resulted in premature mechani(cid:173)
`cal failures/·8 whereas designs with high contact stress
`have led to failures secondary to polyethylene wear.S-11 The
`two basic designs that have stood the test of time (Fig 2) are
`·round-on-flat fixed bearing and meniscal bearing with
`more congruent geometry. Fixed-bearing designs include
`all polyethylene tibial components (Marmor prototype;
`Richards, Memphis, 1N) or metallic-backed polyethylene
`tibial components (Brigham prototype; Johnson and
`Johnson, New Brunswick, NJ), which have been modified
`to allow for cementless fixation and modularity. Meniscal(cid:173)
`bearing designs include the Oxford (Biomet, Warsaw, IN)
`(Goodfellow-O'Connor) cemented straight track constant
`radius and the low contact stress (LCS; DePuy, Leeds, UK)
`radial track with decreasing radius of curvature. The LCS
`provides the option of cementless fixation. Fixed and
`meniscal-bearing knees have been used successfully for
`over 20 years and provide options for the orthopaedic
`
`Operative Techniques in Orthopaedics, Vol8, No 3 (July), 1998: pp 134-14(cid:48)
`1021
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`Fig 1. Ideal candidate for UKA. Typical medial compartment arthrosis with correctable deformity and intact ACL (cartilage loss
`in~tability). Illustrations (A) in extension and (C) in flexion. (B) Intraoperative view in flexion.
`
`s:urgeon who believes in the concept of UI<A. Both fixed
`and meniscal-bearing knees present the s:urgeon with the
`challenge of proper implantation. Basic surgical principles
`apply to all design systems but variations exist.
`More precise instrumentation and improved prosthetic
`design have enhanced the surgeon's ability to achieve a
`better outcome. The initial technique was principally an
`"eyeballing," which has proven to be less than satisfactory
`and is reflected in literature reports. 12 Surgical technique
`and principles of accurate surgical alignment in UKA are
`important factors that are basic to satisfactory outcomes.
`The technique of UKA is more challenging, and experience
`with operative techniques is frequently limited in residen(cid:173)
`cies and/ or fellowships. This paper addresses the technical
`aspects of surgery required to achieve reproducible align(cid:173)
`ment while avoiding the multiple pitfalls inherent in the
`procedure.
`
`from the anteromedial attachment of the patella proxi(cid:173)
`mally along a natural cleavage plane. The distal retinacu(cid:173)
`lum (with the vastus medialis obliqus) is grasped with a
`tenaculum and turned down, exposing the medial con(cid:173)
`dyle. A limited medial sleeve release of the upper tibia
`enhances the exposure. The status of the lateral and
`patellar femoral compartments can be assessed without
`everting the patella. Patella eversion and extensive expo(cid:173)
`sure are not required in UKA. However, if the surgeon is
`more comfortable with a more extensive exposure, it is
`easily accomplished with the midvastus approach. The
`advantages of patella translocation include minimizing the
`external tibial rotation and protecting the normal articular
`cartilage. Maintaining the bulk of the medial quadriceps to
`the central tendon allows for better patella control intraop(cid:173)
`eratively, less postoperative pain, and more rapid rehabili(cid:173)
`tation.
`
`SURGICAL APPROACH
`
`Medial UKA
`
`A midline anterior skin incision is preferred. The incision is
`angled distally to the medial side of the tibial tubercle.
`Minimal undermining is required. The arthrotomy incision
`can be performed through the standard parapatellar, sub(cid:173)
`vastus, or the midvastus variation, which is the current
`approach of choice. The midvastus approach, popularized
`by Engh et al,13 splits the medial quadriceps and capsule
`
`UNICOMPARTMENTAL ARTHROPLASTIES
`
`Lateral UKA
`Lateral compartment replacement for valgus instability is
`best performed through the direct lateral approach, 14-16
`which accomplishes the lateral release with the exposure.
`The skin incision is proximal midline ending distally at a
`point between Gerdy' s tubercle and the tibial tubercle. The
`arthrotomy incision splits the retinaculum (superficial
`layer) at the medial border of Gerdy' s tubercle and extends
`proximally, 1 to 2 em lateral to the patella. The deep
`capsular layer is released from the patellar rim. The
`
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`A Fixed Bearing
`
`8
`
`Meniscal Bearing
`
`Tibia
`All-Poly
`
`Tibia
`Metal-Backed
`
`Cement
`
`Cement
`or
`Cementless
`
`Fig 2. UKA prototypes.
`(A) Fixed-bearing design,
`all polyethylene and
`metal-backed tibia, ce-
`mented or cementless.
`(B) Meniscal bearing de-
`sign, Oxford (cemented)
`and LCS (cemented or ce-
`mentless).
`
`Q..~ford
`
`Cement
`
`LCS
`
`Cement
`or
`Cementless
`
`proximal arthrotomy can be completed by splittjng the
`vastus lateralis or a limited lateral parapatellar incision
`made obliquely through the central tendon. The iliotibial
`band is released in sleeve. fashion from the upper tibia (as
`.required) to enhance exposure of the posterolateral comer.
`Oosure in flexion allows for precise soft-tissue adjustment
`of the prepared layers.
`The direct lateral approach allows for direct soft tissue
`release, adequate. exposure without everting the patella,
`improved patellofemoral tracking, minimal soft tissue
`trauma, and rapid rehabilitation. The approach can be
`extended if TKA is required. The standard medial ap(cid:173)
`proach can be used but has many disadvantages in lateral
`U:KA, including (1) a required extensive approach; (2)
`accentuated external tibial rotation, which may influence
`technique and instrumentation; (3) limited component
`visualization during trial reduction; and (4) less than
`optimal patella tracldng, necessitating a lateral release.
`
`BONE RESECTIONS
`
`Position and Orientation Variables
`
`Effective instrumentation should reliably establish the
`correct size, position, and orientation of the femoral and
`tibial components. The variables of axial rotation, varus(cid:173)
`valgus tilt, flexion-extension orientation, anteroposterior
`(AP) position, and joint line level must be correctly defined
`by the surgeon by using instruments designed for these
`purposes. Proper flexion-extension gap balancing should
`allow for unimpeded motion with normal kinematic con(cid:173)
`trol. Bone resections are the key element in preparing
`implantation surfaces and dictate final positioning. The
`potential for malresection exists on both femoral and tibial
`sides (Fig 3) and will be described later in more detail.
`
`136
`
`Errors are compounded if instrUl:nent malposition (malre(cid:173)
`section) iS made on both sides and. are more common with
`anatomic variations, such as flared femoral condyles,
`which may be a contradiction to UKA.
`Tibial first or femoral first approaches can be used,
`depending on the UKA system17,18 and instrumentation
`philosophy I rationale. Most implantation systems/ how(cid:173)
`ever, have similar guidelines, including (1) referencing off
`the subchondral bone, which is more consistent, or a fixed
`point such as the ACL insertion; (2) correct tibial rotation to
`reproduce a perpendicular mediolateral plane with a 7° to
`10° posterior slope; (3} extramedullary instrumentation for
`the tibial resection; and (4) mating the femoral resection to
`the tibial resection plane with appropriate resection blocks.
`Femoral orientation can include either extramedullary or
`intramedullary instrumentation. An intramedullary sys(cid:173)
`tem requires a more extensive approach and violation of
`the femoral canal, both potential disadvantages.
`The principles of bone resection are similar for fixed and
`mobile bearing systems. The follmving description is for
`the LCS mobile bearing UKAsystem, which I have used for
`the past 17 years. The approach is tibia first. illustrations
`are for a medial compartment replacement (left), because
`medial compartment replacement represents 90% to 95%
`ofUKAs.
`
`Bone Surface Preparation
`
`Exposure of the tibial plateau is enhanced by a sleeve
`elevation that is adequate enough to allow for exposure
`and removal of peripheral osteophytes to normal anatomy.
`Preservation of the outer meniscal rim is recommended to
`maintain the integrity of the medial sleeve, preserve
`optimal stability, and avoid geniculate vessels.
`Tibial and femoral osteophytes are best removed with a
`
`PETER A. KEBLISH, JR
`
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`Fig 3. Bone resection (prosthetic position) variables In flexion. Mal resections are compounded if AP or sagittal plane rotation
`cuts are less than ideal, if femoral geometry is atypical (ie, flared), or gaps unequal. (A) Ideal; (B) internal rotation of the femoral
`component; (C) external rotation of the femoral component; and (D) flared condyle with component position variables. Circular
`insets illustrate tibial varus-valgus malposition.
`
`UNJCOMPARTMENTAL ARTHROPLASTIES
`
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`reciprocating saw and/ or rongeurs to reestablish premor(cid:173)
`bid anatomy. External tibial rotation will improve access to
`the posterior corner. Loose bodies or remaining posterior
`osteophytes are removed. Anatomic variants, pathological
`erosions, the tibial slope, and bone quality are assessed.
`Articular (cartilage and bone) high points or irregularities
`should be removed to subchondral bone because referenc(cid:173)
`ing is more accurate and the .bone surfaces are more
`accessible for instrumentation.
`
`anterior tendon is easily palpable and centers over the
`midpoint of the talus. This point is slightly medial to the
`midpoint of the malleus and centers over the second
`metatarsal when the foot is normal. Medial rod placement
`will result in a valgus position, and lateral rod placement,
`which is more common, will result in a varus position. An
`ideal (perpendicular) resection is critical, therefore
`the alignment rod should be rechecked before final resec(cid:173)
`tion.
`
`THE TIBIAL "L" RESECTION
`
`Flexion-Extension (AP) Alignment
`
`General Principles
`
`Accuracy of the tibial resection is critical and is determined
`by proper instrument positioning for variables of rotation
`(coronal plane), varus-valgus tilt, flexion extension (AP
`slope), horizontal limit (sizing), and depth of resection.
`Rotational orientation influences varus-valgus and the AP
`positions (posterior slope) and therefore should be estab(cid:173)
`lished first. Malposition of the rotational setting can lead to
`subtle or obvious changes in the varus-valgus and AP
`slope cuts, which may lead to less than ideal resections.
`Malresections will result in higher contact stress at the
`articulating surface and increased torque forces at the bone
`(cement) prosthetic interface, especially in fixed beru.ings
`with round-on-flat or dished geometries.
`
`Tibial Res.ection Guide Positioning
`Extramedullary guide systems are the norm because ACL
`preservation is a requitem{;!nt for UKA. Standard TKA
`alignment systems can be used, but extensive e;,cposure. is
`required. Lower profile UKA tibial. resection guides; as
`)Jsed in the LCS system, allow for instrumentation with
`more limited compartment exposure as recommended;
`The resection guide should allow for small adjustments of
`the alignment ·rod to fine tune rotation and the varus(cid:173)
`valgus and AP positions. The guide should allow for an
`adjustable resection block to accommodate the depth of
`resection changes (Fig4).
`
`Rotation Alignment
`The sagittal plane of the "l:' resection djctates the rota-(cid:173)
`tional orientation of the tibial component; therefore,. this
`setting is primary: The alignment rod (with resection block)
`is fixed to the tibial spine proximally and to the ankle
`positioning clamp distally. The rod is set over the tibial
`crest or proximally at the medial border of the tibial
`tubercle, which are the most consistent rotational land(cid:173)
`marks. More medial rod alignment will result in an
`internally rotated tibial component, whereas more lateral
`rod alignment will result in an externally rotated compo(cid:173)
`nent. Both errors will result in rotational malalignment that
`·will be accentuated with the knee in extension.
`
`Varus-Valgus Alignment
`The mediolateral resection should be made perpendicular
`to the anatomic (mechanical) axis of the tibia. The align(cid:173)
`ment rod is best referenced distally (ankle level) to the
`tibialis anterior tendon. The lateral border of the tibialis
`
`138
`
`Reproducing the patient's normal posterior slope (5° to
`10°) is the goal and is important for restoration of normal
`kinematics of the ACL/posterior cruciate ligament (PCL)
`and the so-called four-bar linkage. Alignment systems
`should allow for AP adjustment. The LCS resection block is
`set for a 7o posterior resection when the alignment rod is
`parallel to the tibial crest and/or fibular shaft as viewed
`from the lateral side. Anterior placement of the rod will
`increase the posterior slope whereas posterior rod align(cid:173)
`ment will decrease the posterior slope. Some "eyeballing"
`may be required if external landmarks are obscured.
`Remember that a neutral or decreased posterior slope will
`limit rollback and flexion, increase contact stress on the
`posterior bearing surface, increase polyethylene wear, and
`increase the potential for prosthetic lift off and prosthetic
`fixation failure.
`
`Depth of Re.section
`The depth of r¢sec:tion is best detern:Uned after ha~ing
`confirmed the other variables. The goiU is to resect enough
`bone to allow space J'or the "total tibial prosthetic thick(cid:173)
`ness'' withoutelevating the joint line (femoral-tibial articu.(cid:173)
`l~ting surface). The most consistent landmarks for establish(cid:173)
`ing the proper depth of resection are the ACL insertion and
`the upper slope of the tibial spine. The final joint line
`(articUlating interface) should be located at this level to
`allow for optimal kinematics. The tibial resection block is
`adjusted to a level that accommodates the prosthetic space
`requirement. The level is estimated with a stylus o:~;,
`preferably, an accurately sized tibial drill guide/template
`(Fig 5). The minimal resection approach is frequently
`recommended and has resulted in failures secondary to
`overcorrection, jointline elevation; increased polyethylene
`wear, fixation, patella impingement, etc, and should be
`avoided. The space is more fmite in UKA (ACL-PCL
`controlled) and relates most critically to the normal oppo(cid:173)
`site compartment.
`The "L" resection is completed after all of the variables
`have been checked and fine tuned. Minor malalignments
`can be acceptable, especially in round-on-flat, fixed(cid:173)
`bearing systems that usually "trough out'' the polyethyl(cid:173)
`ene along the rotational arc (from flexion to extension) over
`time.17•18 Final selection of the tibial component size is
`determined after the "l:' resection. Optimal peripheral
`bony rim contact should be obtained with abutment of the
`sagittal tibial surface against the vertical arm of the "L"
`resection (Fig 6). Minor adjustments can be made if the
`depth of resection changes~ The ACL insertion must be
`preserved and the final tibial articulating surface adjusted
`
`PETER A. KEBLISH, JR
`
`WMT 1021-5
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`

`A
`
`B
`
`Tibial
`Crest
`
`Fig 4. (A) Front and (B) side views of tibial plateau instrumentation; setting the tibial resection guide (block).
`
`to the original tibial plateau surface. The spacer block of
`appropriate size and depth is inserted to check all tibial
`resection variables. A drop rod attached to the guide
`rechecks the varus-valgus and the AP slope (Fig 7).
`Ranging the knee from 90° to full extension rechecks the
`level and orientation of the tibial resection and maps the
`rotational tracking to the femoral surface before instrumen~
`tation of the femoral side. The tibial resection should be
`rechecked when the femoral resections are referenced
`from the tibia, and vice versa if a femoral first approach is
`used.
`
`FEMORAL PREPARATION AND SIZE
`SELECTION
`The femoral condyle is frequently irregular with bony
`and/ or articular cartilage high spots. Referencing from the
`subchondral bone is more consistent and is recommended
`
`UNICOMPARTMENTAL ARTHROPLASTIES
`
`with use of most instrument systerri.s, whether a femoral
`first or tibial first approach is used. If not performed
`previously, removal of high spots, including the posterior
`femoral condyle, is now accomplished with use of an
`oscillating saw. Flattening of the subchondral surface
`allows for better seating of alignment shells or cutting
`jigs.
`Femoral size selection, which best approximates the
`existing bony geometry, is initially estimated by use of an
`AP template and mediolateral sizing shells (Fig 8). The
`profile of each template and shell matches the geometry of
`the corresponding implant. It is important to keep in mind
`that it is the shape of the subchondral bone and not the
`articular cartilage which is to be reestablished. Rotational
`(coronal and sagittal) planes are checked. Care must be
`taken to avoid overcorrection and oversizing, which in(cid:173)
`creases the risk of soft tissue and I or patella impingement.
`The medial and lateral prosthetic borders should lie within
`
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`Fig 5. Final tibial positioning. The adjustable resection block sets the depth and AP and rotational planes. The ACL insertion
`approxiinates the joint line al'ld is a consistent reference point.
`
`the femoral condyles. The most superior medial edge is
`often flush with the condyle in the typical medial UKA.
`Overhang must be avoided_. F1ared condyles ll).ay present a
`prob1em. The anterior edge of the prosthesis must be
`placed at a point between the ebumated arthritic bone and
`
`the normal articular cartilage of the femoral trochlea. This
`point can be marked with the knee held in full extension.
`Sizing shells, templates, and the final prosthesis must not
`encroach beyond this point because patellofemoral im(cid:173)
`pingement may occur. Checking the position from flexion
`.
`.
`.
`
`8
`
`. ·-- Final
`}-Implant
`· Thickness
`
`Fig 6. Completed tibial "L" resection. (A) Template/drill guide confirms positions and (B) joint line level.
`
`140
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`PETER A. KEBLISH, JR
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`

`Fig 7. After selection of
`tibia size and thickness,
`varus, valgus, and AP
`tibial slope are checked
`by using a drop rod in (A)
`extension and (C) flexion.
`Rotational mapping ofthe
`tibial trial spacer to the
`femoral condyle from (C)
`flexion to (A) extension,
`with patella reduced, (B)
`will confirm the proper
`orientation and tracking
`of the femoral compo(cid:173)
`nent to the .tibial bearing.
`
`to extension will minimize the potential for anterior im(cid:173)
`pingement problems.
`
`FLEXION-EXTENSION GAP BALANCING
`The AP femoral position (resection) dictates the flexion
`gap, and the distal position dictates the extension gap (Fig
`9). Condylar resections (thickness) must accommodate the
`prosthetic mass. Checking the flexion and extension gap
`with a shell positioner assures that the proper amount of
`bone is resected. If the flexion gap is tight, the sizing
`template can be moved anteriorly to, but not beyond, the
`limiting point described previously. Downsizing the femo(cid:173)
`ral component may be required if the flexion gap is too
`tight or there is anterior impingement. It is important to
`recognize this potential error before femoral resection,
`although it can be corrected after trial component place(cid:173)
`ment. Reattachment of the resection block, however, may
`be less exact, the recuts may be less precise, and the final fit
`possibly compron:tised if previous fixation holes need to be
`redone.
`
`FEMORAL ROTATION CONSIDERATIONS
`
`The femoral component can be placed correctly, too far
`medially or laterally, internally or externally rotated (coro(cid:173)
`nal plane), and flexed or extended (sagittal plane). Malrota(cid:173)
`tion will be exacerbated if these resections are additive
`and/ or combined with tibial malpositioning. As previ(cid:173)
`ously noted, these potential errors can be recognized by
`mapping the rotation plane from90° to 0°. This will avoid
`the initial mal resections as shown in Fig 3. Internal malro(cid:173)
`tation of the femoral component will result in (1) high(cid:173)
`contact stress on the more central articulation, (2) increased
`torque on the prosthetic component, (3) flexion gap instabil(cid:173)
`ity, and (4) rotational incongruence in extension. External
`malrotation will result in (1) high-contact stress on the
`peripheral articulating surface, (2) increased torque, (3)
`flexion gap instability, and (4) increased potential for
`soft-tissue impingement caused by proximal overhang of
`the prosthesis. Flexion positioning of the femoral compo(cid:173)
`nent will result in bearing impingement anteriorly in
`extension. Conversely, extension positioning of the femoral
`
`UNICOMPARTMENTAL ARTHROPLASTIES
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`(setting on high points), the distal resection will be inad(cid:173)
`equate and/ or rotationally malaligned. These malposi(cid:173)
`tions will result in a tight extension gap with overcorrec(cid:173)
`tion and overload of the opposite compartment and I or an
`abnormal articulation at the prosthetic interface. Final
`positioning of the femoral cutting block must be checked
`with the patella relocated to avoid malpositioning and
`malresection. The patella can be dislocated or translocated
`for improved exposure once the resection block setting has
`been confirmed. Resections are completed, and a drilling
`guide is impac1ed, oriented to the lined tibial template.
`Femoral referencing is accomplished with the LCS resec(cid:173)
`tion block as an extramedullary approach. Systems that use an
`intrrunedullary approach also reference the anatomic femo(cid:173)
`ral axis and the anterior femoral cortex. Both systems
`work. Understanding the principles is most important
`because anatomic variances may require fine adjustments,
`which are more technically subtle with UKA than TKA.
`
`FINAL POSITIONING AND TRIAL
`REDUCTION
`After resections (distal, posterior, and chrunfer), a femoral
`drill guide (Fig l1) is impacted to ensure proper fit. The
`knee flexion is ranged from 90° flexion to 0° extension, and
`the final mediolateral and rotational positions are checked.
`The drill guides are set and fixation drill holes are com(cid:173)
`pleted on the femoral and tibial sides (Fig 12A). The trial
`tibial component should pe inserted first, followed by the
`bearing and the femoral component. Final impaction will
`position the tibial component against the sagittal resection
`(Figure 12}3). A stemme.d UI)it, such as theLCS, may requi;re
`rotatiomu maneuvering. External rotation of the tibia will
`aid in exposure and insertion of the tibial component. The
`bearing is inserted by placing a valgus stress from flexion
`to extension and back to extension to clear the femoral
`condyle. The femoral component is then impacted, begin(cid:173)
`ning at 100° and completed with the knee at 60° to 70°
`(Figure 12C). The patella is then reduced and the knee
`ranged from extension to maximum flexion. Normal,
`natural range of motion with meniscal bearing movement,
`anterior in extension and posterior in flexion, confirms
`normal kinematic control. There should be no patella
`impingement and no component liftoff from either tibial or
`
`Fig 9. Flexion-extension. gaps should be equal and parallel.
`(A) The distal position dictates the extension gap and (B) the
`AP femoral position dictates the flexion gap.
`
`PETER A. KEBLISH, JR
`
`B
`
`Fig 8. Femoral size is selected by using the appropriate dimen(cid:173)
`sion determined by the (A) ML and (B) AP position. The
`patella rnust be reduced before rotation check. Component
`positioning is reconfirmed by (A) taking the knee to (C) full
`extension.
`
`component will result in bearing impingement posteriorly
`in flexion. Lateral (central) positioning will result in im(cid:173)
`pingement on the tibial spine; whereas medial (peripheral)
`component positionin_g will result in medial tibial compo(cid:173)
`nent overload. Both will increase the potential for patella
`and/ or medial soft tissue impingement. These mah·ota(cid:173)
`tions (malresections) may lead to increased wear and
`loosening, the primary cause of failure in UKA.
`
`FEMORAL RESECTION
`Coronal plane orientation or axial rotation of the femoral
`component must align to the tibial component in flexion
`and extension. Proper femoral shell placement correctly
`orients the femoral resection block and allows for accurate
`femoral cuts (Fig 10). The resection block should be
`oriented to the femoral axis and allow for proper flexion(cid:173)
`extension position (l'eferencing parallel to the anterior
`femoral cortex). Care should be taken to set the resection
`block flush to the subchondral bone. If the block is proud
`
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`
`

`

`Fig 10. Femoral resec(cid:173)
`tion block setfor (A) dis(cid:173)
`tal, (B) chamfer, and (C)
`posterior cuts with the pa(cid:173)
`tella relocated.
`
`Cut(A)
`
`Posterior Cut(C)
`
`femoral.sides with extremes of motion. The most common
`cause of liftoff or a tight flexion block i,s failure to slope the
`AP resection 7o to 10° as recommended. Fine tuning of any
`resection variables should be completed before permanent
`prosthetic placement.
`
`PERMANENT CQI\IIPONENT
`PLACEMENT/CLOSURE
`After trial componentremqval, final bone bed preparation
`is completed. If cementless fixation is used, the tourniquet
`is released. Bard, sclerotic zones should be drilled. Bone
`paste/slurry collected from drilling and saw cuts is ap-
`
`plied to any tibial and/or femoral surface defects. The
`surface-coated (porous coat, hydroxyapatite) implants are
`impacted for an futerferente fit. If cement fixation is used,
`bone surfaces are thoroughly cleansed and, d,tied before
`cementing. The patella is re:duced. after prosthetic inser(cid:173)
`tion. Mobility and stability are rechecked and soft tissue
`closure accomplished ~ton:rica]:ly, preferably fu flexion,
`which allows optimum range of motion for the soft tissue
`sleeve. Use of suction drainage is prefen'ed butless critical
`fu UKA because bleeding is m:fuimal. Range of motion
`from oo to maximum (normal) flexion is checked after deE!p
`retinacular and skin closure, A bulky pressure dressfug is
`applied to allow for early range of motion with or without
`
`Femoral Drilling
`TempJate
`
`Fig 11. After resection
`femoral drill guide is
`impacted. Rotation
`is
`checked from 90° to 0°.
`
`UNICOMPARTMENTAL ARTHROPLASTIES
`
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`

`c
`
`Fig 12. (A) After fixation holes have been drilled, (B) tibial trial reduction is completed. (C) The tibial bearing is inserted,
`followed by Insertion of the trial femoral component.
`
`continuous passive movement. Ambulation is on the first
`postoperative day and an expedited routine TKA protocol
`is followed with usual discharge by postoperative day
`three.
`
`DISCUSSION/SUMMARY
`UKA remains controversial and its application varies from
`country to country, region to region, and within orthopedic
`trcii:ni:ng centers. Literature reports have been variable,
`ranging from negative studies of Insall and Aglietti, 12
`Laskin, 19 and Swank et al,2° to multiple positive studies.2-
`4.21·26 Advocates of UKA cite the multiple advantages
`which include (1) restoration of normal kinematics; (2)
`preservation of normal structures; (3) avoidance of major
`problems reported with TKA; (4) maintaining and/or
`improving functional range of motion, which is frequently
`decreased after TKA; (5) lower morbidity with no need for
`blood transfusions, less soft tissue damage, etc; and (6)
`lower prosthetic costs and shorter hospitalization. Nonad(cid:173)
`vocates of UKA cite higher failure rates, problems of
`selection and technique, .and difficulty in revision to TKA.
`Conversion of UKA, however, is reported to be less
`
`difficult than revision TKA,27·28 which is also my personal
`experience.
`All authors agree that patient selection and prosthetic
`design can influence outcomes. Grelsamer and Cartier29
`stressed that UKA is not "half a total knee", with major
`differences mostly related to technical factors which have
`been discussed and illustrated. The Swedish knee study8·30
`reported improved results of a large series of UKAs (1,969
`cemented Marmor fixed-bearing UKAs) relative to the
`time of i