Radiographic assessment of the postoperative knee

    Radiographic assessment of the postoperative knee Yara Younan, Philip Kin-Wai Wong, Jean Jose, Ty Subhawong, Michael Baraga, Monica Umpierrez, Adam Daniel Singer PII: DOI: Reference:

S0899-7071(16)30187-5 doi: 10.1016/j.clinimag.2016.11.014 JCT 8155

To appear in:

Journal of Clinical Imaging

Received date: Revised date: Accepted date:

19 September 2016 4 November 2016 16 November 2016

Please cite this article as: Younan Yara, Wong Philip Kin-Wai, Jose Jean, Subhawong Ty, Baraga Michael, Umpierrez Monica, Singer Adam Daniel, Radiographic assessment of the postoperative knee, Journal of Clinical Imaging (2016), doi: 10.1016/j.clinimag.2016.11.014

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Radiographic Assessment of the Postoperative Knee

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Yara Younan, M.D. a* Philip Kin-Wai Wong, M.D. a Jean Jose, D.O. b Ty Subhawong, M.D. b Michael Baraga, M.D. c Monica Umpierrez, M.D. a Adam Daniel Singer, M.D. a

of Radiology and Imaging Sciences, Emory University Hospital, Atlanta, GA. b Department of Radiology, University of Miami, Miami, FL. c Department of Orthopedic Surgery, University of Miami, Miami, FL.

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a Department

Author: Yara Younan, M.D. Emory University Hospital Department of Radiology and Imaging Sciences Section of Musculoskeletal Imaging 59 Executive Park South, 4th Floor Suite 4009 Atlanta, GA 30329 E: [email protected]

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* Corresponding

For the review in Clinical Imaging only

ACCEPTED MANUSCRIPT Abstract: Radiologists often encounter postoperative knee radiographs lacking any adjunct clinical

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data which might hinder accurate image interpretation. Surgical techniques are constantly

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evolving with new devices being used which make it sometimes challenging for the radiologist

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to deduce the performed procedure and to look for associated complications. This article reviews commonly performed surgical procedures of the knee, highlights their expected postoperative

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radiographic appearance and describes the appearance of certain postoperative complications.

Keywords: Postoperative knee; Radiograph; Surgery; Devices; Complications

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Abbreviations: ACL (anterior cruciate ligament); PCL (posterior cruciate ligament); OATS (osteochondral autograft transplant system)

1. Introduction

ACCEPTED MANUSCRIPT Postoperative knee radiographs are frequently encountered by radiologists for a variety of reasons yet the interpretation of these images can be challenging due to evolving surgical

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techniques and frequent unavailability of detailed clinical/surgical history. These radiographs

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may be encountered following the management of a variety of clinical scenarios including repair or reconstruction of soft tissue structures injured during sporting activities, reduction of fractures,

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reconstruction of articular surfaces and, especially in a tertiary care setting, management of

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osseous tumors. By becoming familiar with the expected postoperative appearances of common orthopedic procedures, the radiologist can provide more informative reports, better assess

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adequacy of healing, and more accurately detect complications. This is especially important if no prior studies or operative history is available at the time of image interpretation. While a

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comprehensive discussion is beyond the scope of this article, it aims to describe commonly performed surgical procedures of the knee joint, their expected postoperative radiographic

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appearances and the appearance of certain postoperative complications. This article focuses on findings seen in the adult population, which might be distinct from those detected in the pediatric, nonskeletally mature patient.

2. Discussion 2.1. Sports Injuries 2.1.1. Anterior Cruciate Ligament (ACL) Reconstruction The ACL is one of the most frequently injured ligaments of the knee as a result of sporting activities. It is usually injured from noncontact motions that involve a pivot shift or deceleration with the quadriceps maximally contracted and the knee fully extended [1]. Damage

ACCEPTED MANUSCRIPT to this ligament can also occur in the setting of contact sports when the lower extremity is firmly planted and a forceful torque is applied, such as that seen in “clipping” [1]. The majority of ACL

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ruptures are treated with a reconstruction that necessitates removal of the torn ends of the ACL,

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drilling of femoral and tibial tunnels, and graft ligament placement and fixation. Reconstructions make use of either an allograft that is taken from a cadaver or an autograft that is harvested from

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the patient. Among the autograft options, the two most widely harvested grafts are the bone-

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patellar tendon-bone and hamstring [2]. The bone-patellar tendon-bone graft is composed of the central third of the patellar tendon with bone plugs from the patella and the tibial tubercle, while

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the hamstring graft is harvested from the musculotendinous insertions of the semitendinosus and the gracilis tendons to the tibia. One radiographic clue that a bone-patellar tendon-bone autograft

inferior patella.

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was harvested is a cortical defect or irregularity in the center of the tibial tubercle and in the

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Regardless of graft selection, proper positioning of the femoral and tibial tunnels is crucial to allow for a normal range of motion between flexion and extension, and to prevent graft laxity or notch impingement [3, 4]. Typically, the ideal approach is to drill the tunnels in a way to maintain normal anatomic positioning of the graft. There has been extensive debate regarding the correct radiographic evaluation of the position of the tunnels in reconstructions [5-15], but the clock face analogy remains the most used by radiologists to date. In the majority of ACL reconstructions, surgeons have used the single-bundle technique in which reconstruction of the anteromedial bundle of the ACL is performed without reconstruction of the posterolateral bundle. As such, on an anteroposterior radiograph, if one imagines the intercondylar notch as a clock face with the apex of the notch at the 12-o’clock position, the femoral aperture should be located between the 10- and 11-o’clock positions in the right knee and the 1- and 2-o’clock

ACCEPTED MANUSCRIPT positions in the left knee (Fig. 1A and Fig. 2A) [6, 13]. On the lateral view (Fig. 1B and Fig. 2B), the femoral aperture should be located at a point where the physeal scar meets the posterior

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cortex of the distal femoral diaphysis at the posterior aspect of the Blumensaat line (roof of the

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intercondylar notch) [6, 13]. Certain institutions, however, are resorting to the double-bundle reconstruction that focuses on repairing both ACL bundles by drilling two femoral and two tibial

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tunnels. Postoperative anteroposterior radiographs will show an additional femoral aperture

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between the 9- and 10-o’clock positions in the right knee and the 2- and 3-o’clock positions in the left knee [15]. As for the tibial tunnels, they should be assessed on lateral radiographs and are

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oriented parallel to Blumensaat line with their apertures located completely posterior to it.

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In addition to the graft tunnels positions, the size of the tunnels should be assessed

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radiographically [16]. Typical grafts measure between 8-10 mm in diameter and the tunnels are usually drilled to accommodate a graft of this size. Increasing tunnel diameter over subsequent

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radiographs suggests osteolysis of the graft tunnel (Fig. 3A-B). In the event of a tear of the ACL graft, if a graft tunnel has become too wide as a result of osteolysis, staged surgery may be required. The tunnel would first have to be filled with bone graft and allowed to heal and a second surgery is later performed to reconstruct a new ACL with new tunnels drilled through the area of healed bone graft. Such a staged revision is only required when one or both of the graft tunnel apertures are located in their anatomic position and the tunnels are too wide. Therefore, if osteolysis is present but the ACL graft tunnels were not initially placed in their anatomic location, staged surgery may not be required (Fig. 3C). Fixation devices are yet another feature of ACL reconstructions that requires radiographic evaluation. Grafts are often secured within the femoral and tibial tunnels by aperture (intra-articular) or non-aperture (suspensory, extra-articular) fixation devices [17].

ACCEPTED MANUSCRIPT Aperture fixation secures the graft at the opening of the bone tunnel and usually utilizes interference screws that can be metallic (radiopaque) or bioabsorbable (radiolucent). It is

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important to confirm proper positioning of these interference screws as proud screws (Fig. 4)

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may cause damage to the surrounding tissues especially if they back out into the joint [18]. Nonaperture fixation suspends the graft using a cortical button and an associated suture through

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which the graft is placed. These buttons are usually Endobuttons (Smith and Nephew) that

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should be flush against the adjacent cortex. The femoral Endobutton should be located adjacent to the lateral femoral epicondylar cortex (Fig. 2A-B). It should not be seen in the tunnel on

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anteroposterior radiographs or project over the patellofemoral compartment on lateral radiographs (Fig. 3A-B). Additionally, cross-pin fixation devices (transfixation pins) such as the

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of the femur [13].

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Bio-Transfix (Arthrex) can be used and should be oriented perpendicular to the graft at the level

2.1.2. Posterior Cruciate Ligament (PCL) Reconstruction When compared to the ACL, the PCL is less frequently injured. In general, a PCL injury results from a direct blow to the tibia when the knee is flexed (dashboard injury), a fall on a flexed knee (most commonly seen in soccer), or knee hyperextension [19, 20]. PCL tears are also associated with multi-ligamentous injury patterns usually seen in the setting of a dislocation [21]. When injured, the PCL may be treated non-operatively or may be reconstructed, though the indications for surgical management are beyond the scope of this article. Similar to the ACL reconstruction, a PCL reconstruction involves the drilling of femoral and tibial tunnels in their anatomic location. On postoperative radiographs, the appearance of the tunnels depends on

ACCEPTED MANUSCRIPT whether a single- or double-bundle graft was used. In the single-bundle technique, reconstruction of the anterolateral bundle of the PCL is performed without reconstruction of the posteromedial

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bundle. Using the clock face method in the frontal plane, the femoral aperture should be located

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at the 1-o’clock position in the right knee and at the 11-o’clock position in the left knee (Fig. 2A and Fig. 5), and should be 8-10 mm proximal to the articular surface [22]. In the setting of a

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double-bundle graft technique, an additional aperture will be seen at the 3-o’clock position in the

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right knee and the 9-o’clock position in the left knee [22]. On a lateral radiograph, the singlebundle femoral aperture should be located along the anterior half of the Blumensaat line (Fig.

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2B), and if a second bundle was used, its aperture should be located along the posterior half of the Blumensaat line [22]. The tibial aperture should be located along the posterior half of the

radiographs.

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PCL facet, which will appear as the far posterior aspect of the tibial plateau on lateral

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Two types of tibial fixations techniques have been used to reconstruct the PCL [20, 23] and they can be differentiated by their postoperative radiographic appearance. The first method is the transtibial approach whereby an extra-articular tunnel is drilled through the tibia, passing anterior to posterior to reach the PCL facet. To reach the femoral aperture, the graft has to make a near 90 degree turn, which is sometimes referred to as the “killer curve” and that has been shown to increase the risk of graft failure [24]. The second method makes use of an intraarticular arthroscopic approach whereby the graft is pinned directly to the PCL facet without drilling a tibial tunnel. This tibial inlay technique thus bypasses the need for the "killer curve.” Determination of whether a transtibial or a tibial inlay technique was used can be confirmed by looking for the presence of a tibial tunnel on postoperative radiographs (Fig. 2A-B and Fig. 5), and for the presence or absence of a device that secures the graft to the tibia. If a transtibial

ACCEPTED MANUSCRIPT approach was used, on the lateral radiograph, the tibial tunnel should pass from anterior to posterior to reach the PCL facet while the femoral tunnel may parallel the trochlear articular

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surface. On the frontal projection, the tibial tunnel should pass in a distal medial to proximal

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lateral direction while the femoral tunnel should curve in a distal lateral to proximal medial direction. If a cortical Endobutton is used, the Endobutton should be flushed against the cortex of

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the medial femoral epicondyle (Fig. 2A-B). Similar to the ACL reconstruction, proud screws

2.1.3. Multi-ligamentous Reconstruction

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should be described when present, especially when protruding in an articular surface.

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Multi-ligamentous knee injuries are a relatively rare injury that can result in significant morbidity and functional impairment. Although many of these cases reduce prior to the initial

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clinical evaluation and radiograph acquisition, such injuries usually occur in the setting of knee dislocations with up to 33% of dislocations resulting from sports injuries [25]. In the event of a dislocation, both the ACL and PCL are typically completely torn, with associated disruption of the medial collateral ligament complex and the posterolateral corner [21, 25, 26]. After confirmation of an intact neurovascular bundle, ligamentous reconstruction may be considered to regain stability and function of the knee. In addition to the ACL and PCL reconstructions, some orthopedists may elect to repair or reconstruct other structures such as the posterolateral corner, the medial collateral ligament, or the posteromedial corner structures. Failure to address these concomitant injuries may lead to residual laxity and early graft failures [25, 26]. The relative rarity of multi-ligamentous reconstructions and the extensive hardware used in these procedures can make the assessment of these postoperative radiographs challenging. However, the extensive

ACCEPTED MANUSCRIPT hardware should alert the interpreting radiologist that a multi-ligamentous reconstruction has taken place. The next step would be to identify what ligaments are located near each piece of

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hardware. In the setting of a multi-ligamentous reconstruction, the reviewer should assume that

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at least the ACL was reconstructed and begin with its assessment. The PCL was also likely injured so one should look for PCL reconstruction changes. Next, the medial knee should be

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inspected. Hardware along the course of the medial collateral ligament points to a reconstruction

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(Fig. 6). Finally, screws or screw tracks within the posterior lateral tibia or fibula may indicate a posterolateral corner reconstruction (Fig. 6). Additional screw track or tracks on the medial

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femoral condyle or anterior medial tibial metaphysis may indicate a posteromedial corner

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reconstruction with a semitendinosus autograft [27].

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Similar to other reconstructive surgeries, a multi-ligamentous knee reconstruction carries an increased risk of infection [28]. In the setting of suspected infection, an initial plain

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radiograph might be helpful to evaluate the integrity of the graft tunnels and look for any suspicious soft tissue fluid, effusion, or periarticular decreased bone density or erosions. Osteolysis of a graft tunnel with the presence of an associated fluid collection extending into the surrounding soft tissues should raise suspicion for infection and necessitates further evaluation with an MRI (Fig. 7A-C).

2.1.4. Chondral Injury Chondral flaps and osteochondral fractures are not uncommon in young athletic patients following a twisting force or a direct blow to the knee [29]. Unfortunately, these lesions often fail to heal on their own. Stable regeneration of hyaline cartilage has not been documented with

ACCEPTED MANUSCRIPT the current available treatment options [30]. Conservative, non-surgical treatment focused on symptom reduction is generally reserved for small low grade non-delaminating chondral lesions.

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For more complex cases, surgical intervention may be needed to prevent progressive cartilage

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loss. In general, these surgical interventions fall under two broad categories, debridement and the newer restoration procedures. The purpose of debridement, also known as chondroplasty, is to

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trim down cartilaginous flaps that may progress to large high-grade chondral injuries in the

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absence of intervention. This technique does not restore the articular surface. Especially in adolescents, orthopedic surgeons may also choose to pin large cartilaginous flaps back down to

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the subchondral bone especially if bleeding of the subchondral plate can be induced. Some surgeons may choose to place bone graft beneath the cartilaginous flap. Screw tracts within the

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subchondral bone, especially in the weight-bearing portions of the medial and lateral femoral condyles, should alert the interpreting physician that a surgery has been performed to re-

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approximate a cartilaginous flap (Fig. 8A). One potential complication is that the pinning device may become proud and could irritate the opposing articular surfaces (Fig. 8B-C). Additionally, over time, the pinning device could back out completely and become loose within the joint. Cartilage restoration procedures, on the other hand, attempt to restore the articular surface by regenerating tissue to fill in osteochondral defects [30]. They include marrow stimulation techniques, osteochondral autograft transplant system (OATS) surgery and osteochondral allografting. Several marrow stimulation techniques are available, the most common of which is the microfracture technique although this is often radiographically occult as the holes are too small to see. When osteochondral autografting is performed, the defect is sized and osteochondral plugs from non-weight-bearing articular surfaces (often the margin of the trochlea) are removed and transferred into the defect. This technique results in filling of the

ACCEPTED MANUSCRIPT defect with osteochondral tissue with overlying hyaline cartilage [30]. Radiographically, the interpreting radiologist should recognize the presence of relatively large osteochondral defects

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with sharp margins in both a weight-bearing and a non-weight-bearing surface of the joint (Fig

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9A-C). Similar results can be reached with the osteochondral allograft transplantation surgery

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that makes use of cadaveric tissue instead of tissue from the patient's knee.

2.1.5. Patellofemoral Joint Instability

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Patellofemoral joint instability may manifest as a transient lateral patellar dislocation with the medial aspect of the patella impacting the lateral aspect of the lateral femoral condyle.

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For first-time lateral patellar dislocations, especially in younger patients, orthopedic surgeons may opt for conservative therapy which usually consists of physical therapy [31]. However,

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recurrent patellar dislocation has been reported in up to 44% of patients treated conservatively [32]. In the event of continued dislocations despite conservative management, surgery is needed to correct the anatomic defects predisposing to the instability. The most commonly performed procedure is the reconstruction of the medial patellofemoral ligament, the primary restraint against lateral patellar dislocation in the first 30 degrees of knee flexion [31]. Similar to other reconstructive procedures, the surgeon can choose between allografts or autografts. Regardless of graft selection, reconstruction is performed to parallel the anatomic orientation of the medial patellofemoral ligament. The isometric point for the femoral attachment is usually determined using the radiographic guidelines described by Schottle et al. involving the identification of 3 lines on a lateral radiograph [31-33] (Fig. 10A). The first line is tangential to the posterior femoral cortex and the second is perpendicular to the first, intersecting at the point where the

ACCEPTED MANUSCRIPT femoral condyle contacts the femoral cortex. The final line is also perpendicular to the first line but passes through the most posterior aspect of the Blumensaat line. The isometric point is

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located 1 mm anterior to the first line, 2.5 mm distal to the second, and immediately proximal to

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the third line [31, 33]. When viewing the postoperative radiographs, a tunnel located at this point should alert the interpreter that a medial patellofemoral ligament reconstruction surgery has

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been done. Lateral radiographs will also show 1-2 tunnels within the patella through which the

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graft passes (Fig. 10B). These tunnels should not breach the patellar articular surface. Some patients, however, have persistent instability despite a medial patellofemoral ligament

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reconstruction. If these patients have a tibial tubercle-trochlear groove distance of > 15 – 20 mm measured on CT or MR imaging, a tibial tubercle osteotomy and transfer might be necessary

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[34]. The tibial tubercle is transferred medially and then reattached thus decreasing lateral patellar tracking. If patella alta is present, the surgeon may also translate the patella distally.

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Postoperative radiographs should demonstrate stable anchoring of the tibial tubercle with healing across the osteotomy (Fig. 11 and Fig. 12).

2.1.6. Proximal Tibiofibular Joint Instability Proximal tibiofibular joint instability is a relatively rare knee injury that has been reported to occur both in isolation and in the setting of bony and multi-ligamentous injuries [35]. Dislocation of the joint generally occurs in athletes as a result of a severe twisting motion during knee flexion. Due to its close proximity from the common peroneal nerve, this injury may be associated with peroneal nerve palsy. When assessing the proximal tibiofibular joint with radiographs, the fibular head should overlap the lateral margin of the tibia and should be below

ACCEPTED MANUSCRIPT the lateral joint line on an anteroposterior view [36, 37]. On a lateral view, the fibular head should be posterior to the proximal tibia [36, 37]. It is important though to be mindful of the

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position of the knee as obliquity affects the projection of the fibular head. Since radiographic

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abnormalities of proximal tibiofibular joint instability tend to be subtle, if instability is strongly suspected clinically, additional modalities such as dynamic ultrasound or examination under

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anesthesia could be considered. If identified early, isolated proximal tibiofibular joint instability

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can be managed with closed reduction and immobilization or open reduction followed by fixation with Kirschner wires or screws [35, 38]. However, in cases of delayed diagnosis,

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reconstruction may be needed. Postoperative radiographs would show screw tracts in the general area of the proximal tibiofibular joint (Fig. 13). Alternatively, joint arthrodesis or fibular head

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resection could be performed although this should be avoided in athletes [35, 38].

2.1.7. Proximal Fibular Collateral Ligament Avulsion Injury Avulsion fractures of the knee occur in sports-related trauma due to the numerous tendinous and ligamentous attachments. In general, injuries involving the lateral stabilizers of the knee are less prevalent than those involving the medial stabilizers and are often associated with injury to the cruciates and medial meniscus [39]. Despite being rare, proximal avulsion fractures of the fibular collateral ligament can occur. These fractures might even require surgery if patients experience ongoing pain and instability at areas of nonunion, especially in high-performance athletes. Due to the rarity of this type of avulsion injury, no clear treatment guidelines have been established. In general, treatment is dictated by the patient’s stability, level of activity, presence of associated injuries and surgeon preference. Some fractures necessitate open reduction and

ACCEPTED MANUSCRIPT internal fixation with staples [40] while others might require bone grafting and fracture reduction with lag screw fixation. Although the latter results in an unusual postoperative appearance of the

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knee, the location of the screws and the healing fracture fragment should suggest the possibility

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of this type of procedure. When assessing for the success of the surgery, the radiologist should ensure that the hardware is stable and bony bridging is present across the fracture fragment (Fig.

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14).

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2.2. Traumatic Fractures

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2.2.1. Tibial Plateau Fractures

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Tibial plateau fractures are among the more common non-sports related traumatic knee

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fractures requiring surgical intervention. They are classified into six types using the Schatzker system [41, 42]. According to this classification system, in general, an increase in the numeric category indicates an increase in severity. Most tibial plateau fractures begin on the lateral tibial plateau in the setting of a valgus force with concomitant axial loading [42]. As the axial loading increases, more complex fracture patterns may develop to involve the medial tibial plateau, both plateaus or complete separation of the metaphysis from the diaphysis [42]. The goal of surgery in these fractures, especially when associated with surface depression or fragmentation, is to regain articular surface congruency and minimize the risk of posttraumatic osteoarthritis. Due to the high-energy injury associated with these fractures, they frequently occur with internal derangement of the knee that is effectively demonstrated by MR imaging and that may also require reconstruction or repair [42]. Typical postoperative radiographs demonstrate the presence of cancellous screws with a lateral buttress plate reducing the dominant fracture fragments (Fig.

ACCEPTED MANUSCRIPT 15). With more complex fracture patterns, and thus higher Schatzker classification scores, both medial and lateral buttress plates may be present. The presence of double buttress plates should

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alert the reviewer that bicondylar fractures are present and that both articular surfaces should be

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evaluated for congruency. Although uncommon, placement of screws through the articular surface or tibial tubercle would constitute malpositioning and could potentially result in further

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soft tissue damage or pain.

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2.2.2. Patellar Fractures

Patellar fractures can occur with direct impaction or with indirect injury from contraction

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of the extensor mechanism. Treatment is directed toward achievement of patellar articular surface congruency to reduce the risk of posttraumatic patellofemoral joint osteoarthritis and to

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restore the extensor mechanism [43, 44]. Although conservative treatment can be used in specific cases of patellar fractures, unstable ones always require surgical intervention. A number of surgical options have been described, the most common of which are the modified tension band wiring, lag screw fixation and partial patellectomy [43, 45]. In the modified tension band wiring technique, the reduction construct is positioned to convert the distraction forces of the extensor mechanism into compressive forces along the articular surface of the patella [43]. These compressive forces are needed for proper healing. The reduction construct is formed of at least two K-wires or partially threaded cannulated screws placed parallel to each other and perpendicular to the fracture line, with a tension band applied in an eight-shaped manner and tightened intraoperatively. When reviewing postoperative radiographs following the modified tension band wiring reduction (Fig. 16), it is important to assess for the integrity of the tension

ACCEPTED MANUSCRIPT bands as failure may result in loss of the compressive forces and re-creation of the distractive forces along the articular surface, which will promote malunion/nonunion. In general, a revision

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surface congruency is disrupted by more than 2-3 mm [43, 44].

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surgery is required if the fracture fragments separate by more than 3 mm or if the articular

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2.2.3. Distal Femoral Fractures

Fractures of the distal femur usually occur as a result of high-energy injury in a young patient or

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after a fall in older adults. They can be broadly classified as intra-articular or extra-articular [46]. Although various methods have been described to reduce distal femoral diaphyseal fractures

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[47], one of the most commonly used is retrograde intramedullary nailing. Following reduction of the fracture, a nail is placed through the fracture and into the proximal femoral shaft where it

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is secured by interlocking screws (Fig. 17). This procedure aims to restore limb alignment and maintain that position until bone healing occurs [46]. Although infrequent, complications may occur. Interlocking screws ideally should have bicortical purchase. Failure to obtain bicortical purchase can result in backing out of the screw into the soft tissues (Fig. 18). Additionally, similar to other procedures in which a drill bit is used, during drilling and reaming of the medullary canal for a nail placement, drill bits can break off in the bone (Fig. 17) or fracture lines may propagate.

2.3. Degenerative Diseases

ACCEPTED MANUSCRIPT 2.3.1. Arthroplasty Symptomatic osteoarthritis of the knee is a common problem with an estimated lifetime

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risk of 50%, with half of these cases diagnosed by age 55 [48]. After conservative treatment

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fails, many patients resort to arthroplasty to reduce their pain. A comprehensive discussion of

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knee arthroplasties is beyond the scope of this manuscript [49, 50], but in general, treatment options consist of a unicompartmental knee arthroplasty or a total knee arthroplasty. A

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unicompartmental knee arthroplasty (Fig. 19A-D) has the advantage of less morbidity,

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preservation of bone stock, faster recovery and maintenance of the ligamentous structures allowing for normal knee kinematics [51]. Despite these advantages, unicompartmental

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arthroplasty surgery accounts for a mean of 8% of all knee arthroplasties [48]. When performed,

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unicompartmental knee arthroplasty commonly involves the medial tibiofemoral compartment with replacement of the medial femoral condyle and the medial tibial plateau articular surfaces

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[51]. The majority of knee arthroplasties currently performed are thus total knee arthroplasties that usually include patellar resurfacing. When reviewing postoperative knee radiographs, regardless of the arthroplasty type, it is important to confirm that the hardware is appropriately positioned and that there is no radiolucency at the bone-hardware or bone-cement interfaces. Increasing lucency at these interfaces may indicate aseptic loosening, which is more common with tibial components [52]. Additionally, subsidence of the tibial component, its shift into a varus position, or the shift of the femoral component into a flexed position are very reliable predictors of loosening [52]. Although aseptic loosening (Fig. 20A-B) is the most common cause of revision of total knee arthroplasties, loosening could be due to an infection (Fig. 21) [50, 52]. Wear of the polyethylene liner could also occur, resulting in significant narrowing of the knee compartment. Patellar resurfacing components may contain radiopaque markers to help evaluate

ACCEPTED MANUSCRIPT their positioning. In the event of loosening of the patellar resurfacing component, the marker

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may be displaced away from its native position (Fig. 22A-B).

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2.4. Osseous Tumors

Nonneoplastic intraosseous lesions, benign intraosseous neoplastic lesions, benign locally

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aggressive intraosseous lesions, and malignant intraosseous lesions constitute another category of knee joint diseases requiring surgical intervention. Various surgical procedures have been

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developed, the choice of which is dictated by the pathology of the intraosseous lesion. In the case of nonneoplastic, benign and some benign locally aggressive intraosseous neoplastic lesions,

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treatment may consist of curettage, usually in conjunction with bone grafting or cement augmentation to fill the residual cavity (Fig. 23A) [53-55]. When assessing postoperative

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radiographs in such cases, one of the most important things to notice is the appearance of the bone graft/cement bone interface [55]. Increasing lucency within the filling material or surrounding bone suggests tumor recurrence (Fig. 23B). In the setting of malignant intraosseous tumors, en bloc resection of the tumor and surrounding bone may be required [56]. When the tumor is located near the knee, the entire joint may be resected. En bloc resection of the tumor is usually followed by endoprosthetic replacement [57]. Postoperative radiographs of these cases show arthroplasty devices that are not typically used in the degenerative setting, which should alert the interpreting radiologist to the possibility of a previous tumor around the knee. In addition to looking for signs of hardware failure (Fig. 24), it is important to look for signs of tumor recurrence such as bone destruction, increasing soft tissue fullness and developing tumor matrix.

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3. Conclusion When presented with a postoperative knee radiograph, systematically analyzing the type

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and location of the implanted hardware or graft reconstructions allows the radiologist to

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determine the patient’s underlying injury as well as the surgical treatment. This knowledge

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enables more careful scrutiny for procedure-specific complications or evidence of surgical

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failure.

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Funding: This research did not receive any specific grant from funding agencies in the public,

References: [1] [2]

[3] [4]

[5]

[6] [7]

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Acknowledgments: None

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commercial, or not-for-profit sectors.

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Figure 1A-B: 33-year-old male with an ACL bone-patellar tendon-bone autograft

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reconstruction. Anteroposterior (Fig. A) and lateral (Fig. B) radiographs of the left knee demonstrate the typical position of the interference screw containing femoral tunnel (black arrow) and tibial tunnel (white arrow). Figure 2A-B: 42-year-old female with ACL and PCL single-bundle allograft reconstructions. Anteroposterior (Fig. A) and lateral (Fig. B) radiographs of the right knee show the typical position of the femoral tunnel in an ACL (solid white arrow) and PCL (solid black arrow) reconstruction. The tibial tunnels (ACL dotted white arrow; PCL dotted black arrow) are also indicated. Note that even though the femoral endobuttons (ACL white arrowhead; PCL black arrowhead) are not adherent to the cortex, this more distant positioning does not necessitate mechanical failure or symptom occurrence.

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radiographs demonstrate widening of the femoral tunnel (black arrow) with the endobutton

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Figure 3C: Corresponding intraoperative arthroscopic view of the intercondylar notch of the

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patient from Figure 3A-B. Notice the old, non-anatomic femoral aperture (black arrow) and the

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Figure 4: 35-year-old male soccer player with previous ACL ligament tear status post reconstruction. Lateral knee radiograph shows that the tibial tunnel interference screw has

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Figure 5: 35-year-old male status post PCL allograft reconstruction. Anteroposterior radiograph

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of the left knee demonstrates the typical position of the femoral tunnel (black arrow) and the interference screw containing tibial tunnel (white arrow). Note that there is tibial tunnel osteolysis.

Figure 6: 21-year-old male with ACL, medial collateral ligament and posterolateral corner reconstructions. An anteroposterior radiograph of the right knee shows two screws (dotted black arrows) along the course of the medial collateral ligament complex. Screws and screw tracts (solid black arrows) can also be seen in the lateral femur, tibia and fibula indicating a posterolateral corner reconstruction. Also shown is the femoral endobutton (white arrowhead) and the tibial interference screw (dotted white arrow) of the ACL reconstruction.

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containing PCL tibial tunnel (black arrow). Almost a year later, the patient presented with pain

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tunnel (black arrowhead) as well as a soft tissue abscess (dotted white arrows). Also shown is the femoral endobutton (dotted black arrow) and the tibial interference screw (white arrow) of

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Figure 8A: 17-year-old male basketball player with knee pain. Anteroposterior knee radiograph

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demonstrates osteochondral defect in the weight bearing portion of the medial femoral condyle (white arrowhead) and screw tracts (black arrow) in the subchondral bone indicative of a

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previous repair.

Figure 8B-C: Arthroscopic view of the patient from Figure 8A. Upon presentation, the osteochondral defect was probed (Fig. B). Bone was found on the undersurface of the cartilage and was thus considered amenable to grafting. However, the patient continued to experience pain. Repeat arthroscopy (Fig. C) demonstrated a proud screw (black arrow) that had to be removed. Figures 9A-C: 35-year-old male with medium sized osteochondral lesion in the posterior lateral femoral condyle and with ongoing pain despite conservative treatment who underwent OATS. Lateral intraoperative radiograph (Fig. A) shows an osteochondral plug harvested from the nonweight bearing lateral margin of the trochlea (white arrow) which is being inserted into the

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Figure 10A-B: 18-year-old female athlete with recurrent patellar dislocations necessitating

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reconstruction of the medial patellofemoral ligament. Intraoperative fluoroscopy of the knee joint (Fig. A) done to determine the isometric point for the femoral attachment of the medial

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patellofemoral ligament. The solid white line is tangential to the posterior femoral cortex. The

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isometric point is depicted as a white circle with the dotted black lines indicating the expected orientation of the graft. Postoperative lateral radiograph (Fig. B) shows the femoral (black

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arrow) and patellar (white arrows) anchors of the medial patellofemoral ligament reconstruction. Figure 11: 17-year-old male status post tibial tubercle osteotomy and transfer 4 days ago. Postoperative lateral knee radiograph shows two screws anchoring the tibial tubercle after its medial transfer.

Figure 12: 16-year-old female status post tibial tubercle osteotomy and transfer nine months prior. Postoperative lateral knee radiograph shows non-union of the transferred tibial tubercle. Figure 13: 62-year-old male with history of chronic instability at the right superior tibiofibular joint. Anteroposterior radiograph of the knee after open reconstruction of the joint demonstrates tracts for the graft screws (black arrows).

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femoral attachment. The orthopedic surgeon opted for decortication of the undersurface of the

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fracture fragment and the adjacent femur followed by bone grafting and fracture fragment reduction with partially threaded cannulated screws. Postoperative anteroposterior radiograph of

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the knee shows osseous bridging proximally with what appears to be cortex centrally.

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Figure 15: 45-year-old female who sustained a tibial plateau fracture in a motor vehicle accident

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necessitating an open reduction and internal fixation surgery. Postoperative radiograph shows threaded screws and a lateral buttress plate. The lateral tibial plateau surface shows near

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Figure 16: 40-year-old female who underwent a modified tension band wiring reduction. Postoperative lateral radiograph shows two K-wires (black arrow) that were used to cross the transverse body fracture. Also shown are the tension bands (white arrowhead) that were applied to create the compressive forces required for healing. Figure 17: 78-year-old female who sustained a distal femoral fracture necessitating retrograde intramedullary nailing. Postoperative anteroposterior radiograph shows three distal interlocking screws, with a retained broken drill bit (white arrow). Figure 18: 50-year-old male status post retrograde intramedullary nailing with new onset pain. Anteroposterior radiograph of the knee shows two distal interlocking screws (white arrows) that have backed out from the partially seen retrograde intramedullary nail.

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Figure 20A-B: 59-year-old female status post right total knee arthroplasty with new onset pain.

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Figure 21: 59-year-old male who had underwent total knee arthroplasty complicated with an

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the femoral component.

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infection and hardware failure. Lateral knee radiograph demonstrates complete displacement of

Figure 22A-B: 56-year-old female who had underwent total knee arthroplasty complicated with an infection and hardware failure. Anteroposterior (Fig. A) and lateral (Fig. B) radiographs of the knee demonstrate loosening of the patellar resurfacing component and its displacement into the joint (white arrow) as well as tilting of the tibial component with surrounding lucency indicative of loosening.

Figure 23A-B: 34-year-old male with a giant cell tumor of the bone in the proximal lateral tibia. Curettage followed by bone grafting and cement augmentation was done as demonstrated by the postoperative radiograph (Fig. 20A). One year later, during surveillance imaging (Fig. 20B), large areas of lucency (white arrow) were seen in the previously treated area suggestive of

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placement of a femorotibial endoprosthesis. Current radiograph shows lucency around the

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Postoperative knee radiographs lacking any adjunct clinical/surgical history are often encountered by radiologists in various settings. Knowledge of commonly performed surgical procedures of the knee and their expected postoperative radiographic appearance is necessary to determine the initial injury and more carefully detect possible associated structural damage. Familiarity with the expected postoperative appearances of the knee facilitates recognition of common procedure-specific complications.

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