Joint intracapsular disorders: diagnostic and nonsurgical management considerations

This article reviews common intracapsular temporomandibular disorders encountered in the dental practice. It begins with a brief review of normal temporomandibular joint anatomy and function followed by a description of the common types of disorders known as internal derangements. The etiology, history, and clinical presentation of each are reviewed. Nonsurgical management is presented based on current long-term scientific evidence.

Shoulder function: the perfect compromise between mobility and stability

Shoulder function is a compromise between mobility and stability. Its large mobility is based on the structure of the glenohumeral joint and simultaneous motion of all segments of the shoulder girdle. This requires fine-tuned muscle coordination. Given the joint's mobility, stability is mainly based on active muscle control with only a minor role for the glenohumeral capsule, labrum and ligaments. In this review factors influencing stability and mobility and their consequences for strength are discussed, with special attention to the effects of morphology, muscle function and sensory information.

The Posterior Segment of the Temporomandibular Joint Capsule and Its Anatomic Relationship

PURPOSE

The aim of this work was to clarify the arrangement of the posterior segment of the temporomandibular joint capsule and its pertinent relationships.

MATERIALS AND METHODS

The temporomandibular region was dissected bilaterally in 20 adult cadavers. Natural stained latex was injected into 16 cadavers through the external carotid artery to facilitate the dissection of the arterial vessels.

RESULTS

The posterior segment of the joint capsule is made up of the so-called "bilaminar zone" of the articular disc. The upper internal portion of the posterior segment of the capsule was reinforced by the discomalleolar ligament. The retroarticular space was filled with loose connective tissue and the anterior branches of the anterior tympanic artery were distributed throughout the posterior segment of the joint capsule.

CONCLUSION

The posterior segment of the temporomandibular joint capsule corresponds to the bilaminar zone of the articular disc. The structures of the retroarticular space are extracapsular.

MR imaging of the intraarticular disk of the acromioclavicular joint: a comparison with anatomical, histological and in-vivo findings

OBJECTIVE

To characterize MRI features of the intraarticular disk of the acromioclavicular joint.

DESIGN

We studied the appearance of 11 acromioclavicular joints of six cadavers (subjects aged 57-89 years at the time of death) and six healthy shoulders on T1-weighted, T2 (TSE)-weighted, STIR and PD (fat saturated) magnetic resonance imaging (MRI) and compared the findings with observations during dissection and histological examination.

RESULTS

Macroscopic examinations showed two wedge-shaped disks underneath the superior and above the inferior joint capsule in nine specimens. In two specimens the acromioclavicular joints were degenerated. Histologically, the disk tissue consisted of fibrocartilage whereas the joint cartilage was partly degenerated, containing zones of fibrocartilage amidst degenerated hyaline cartilage, which may explain the similar signal intensity of both structures in all sequences used. MR appearance of the intraarticular structures of the acromioclavicular joint was similar in cadaveric and healthy shoulders.

CONCLUSIONS

The difficulties related to imaging the acromioclavicular joint may be explained by the anatomy. Similar signal intensity of cartilage and disk may be explained by their similar histological structure (fibrocartilage). MRI findings should be interpreted with respect to the variable anatomy. These results may serve as a basis for further radiological studies of the acromioclavicular joint.

Normal MR imaging anatomy of the elbow

The functional complexity achieved at the elbow is a reflection of the sophisticated architecture that embodies this articulation. In addition to challenging anatomic relationships to conceptualize, there are many anatomic variations that exist in the osseous, capsular, and muscular structures. This article offers a detailed description of the structural and imaging anatomy of the elbow, information that establishes the foundation of imaging interpretation of internal derangements.

Ulnar coronoid process anatomy: possible implications for elbow instability

Ulnar coronoid process fractures are relatively uncommon injuries usually occurring with elbow dislocations and contributing to elbow instability. Recent evidence suggests coronoid tip fractures have a role in the instability. We sought to quantify the capsular and brachialis attachments of the ulnar coronoid process to better understand why instability occurs. We prepared eight fresh-frozen cadaveric specimens to ascertain the specific attachment locations. After dissection, we isolated and resected the proximal ulna, including the coronoid process and its soft tissue attachments. We then embedded, sectioned, and stained the specimens. The average distance from the tip of the coronoid to the proximal capsule was 2.36 +/- 0.39 mm. The average distance from the tip of the coronoid to the proximal brachialis insertion was 10.13 +/- 1.6 mm. Most coronoid tip fractures included disruption of the anterior capsule, which potentially explains why instability can be associated with these fractures.

Distribution of A-delta and C-fiber receptors in the cervical facet joint capsule and their response to stretch

BACKGROUND

It has been proposed that cervical facet joint capsules are a major source of whiplash pain. However, there is a paucity of neurophysiologic data to support this hypothesis. The purposes of this study were to determine the distribution of A-delta and C-fiber sensory receptors in the facet joint capsule and to test their patterns of response to stretch and related sensory function.

METHODS

Laminectomy from C4 to C7 was performed in seventeen goats, while they were under general anesthesia, to expose the C6 nerve roots. Customized dual bipolar electrodes were used to record neural activity from one of the C6 branches. An 8 or 15-V electrical stimulus was used to provoke receptor activity in nine designated areas on the dorsal part of the C5-C6 facet joint capsule. Receptors were classified on the basis of conduction velocities. The waveform of an identified receptor was set up as a template to determine its neural activity in response to capsular stretch. The characteristics of each single receptor's response to capsular stretch were analyzed to determine its sensory function as a mechanoreceptor or nociceptor.

RESULTS

Two hundred and forty-eight receptors on the dorsal part of the C5-C6 facet joint capsule were evoked by electrical stimulation in the seventeen goats. More C-fiber receptors were found on the dorsolateral aspect of the facet joint capsule, where tendons and muscles were attached. The response to stretch of 120 receptors, from twelve goats, were analyzed to classify them into one of four categories (high-threshold mechanoreceptors, non-saturated low-threshold mechanoreceptors, saturated low-threshold mechanoreceptors, and silent receptors) or as unclassified receptors.

CONCLUSIONS

The existence of receptors in the facet joint capsule indicates that the capsule has pain and proprioceptive sensory functions.

Anatomical basis of arthroscopic capsulotomy for elbow stiffness

Stiffness is a frequent condition in elbow pathologies, both traumatic and non-traumatic, and usually requires an operative treatment including an anterior capsulotomy. Elbow arthroscopy is certainly an alternative to surgery, but the technique of arthroscopic capsulotomy remains controversial. Our aim was to study the anterior elbow capsule anatomy to recommend an efficient and safe arthroscopic capsulotomy. We dissected ten cadaveric elbows and analyzed the insertions of the anterior capsule, their variations and the relationships with the surrounding neurovascular structures (radial and median nerve, brachial artery). The influence of elbow flexion was studied on fresh elbows with radioscopic evaluation. The distances between the anterior capsule and the neurovascular structures were measured at four reference levels. The insertions of the anterior capsule were also studied on the embalmed elbows. The radial nerve is always the closest structure to the capsule, but in this study it was always protected by the brachialis muscle. The distance between the anterior capsule and the neurovascular structures is consistently higher on the proximal side, regardless of which structure is considered. The 90 degrees flexion position allows the best capsular distension and offers optimal security with regard to neurovascular structures. All arthroscopic surgeons are concerned about potential neurovascular complications (varying from 0 to 14% in the literature). Previous anatomical studies examined the relationships between the arthroscopic portals and the neurovascular structures. This study developed a precise description of the relationship between the anterior capsule and the surrounding neurovascular structures, which let us recommend technical parameters to conduct a safe arthroscopic capsulotomy.

Nerve endings of the wrist joint: a preliminary report of the dorsal radiocarpal ligament

As part of an investigation of the articular nerve ending populations in the wrist joint capsule associated with the anterior and posterior interosseous nerves, this study addresses the nerve ending population in the dorsal radiocarpal ligament. The ligaments were harvested from four wrists of two fresh cadavers within 12 h of death. Tissues were fixed, cryostat sectioned, and processed for fluorescence immunohistochemistry using antibody to protein gene product 9.5 (PGP 9.5), a general or pan neuronal marker, and a secondary antibody conjugated to a fluorescent tag (Alexa Fluor 488). The sections were evaluated with a confocal laser microscope and an image analyzer. Labeled nerve endings were mapped, measured, and categorized. Type I (Ruffini-like ending), Type III (Golgi-like tendon organ) and Type IV (noncorpuscular) nerve endings could be identified in all four DRC ligaments, with Types I and IV dominating. These receptors were distributed primarily over the superficial two thirds of the ligament (>80%), and near the bony attachments (>70%). The dorsal radiocarpal ligament has a rich sensory innervation from the posterior interosseous nerve terminating in nerve endings located in the superficial two-thirds of the ligaments, primarily near bony attachment sites.

Anatomy and Biomechanics of the Lateral Side of the Knee

The posterolateral corner (PLC) of the knee is a critical element for a functional lower extremity. It consists of an array of complex ligamentous and musculotendinous structures. The primary function of the PLC is to resist varus and external rotation and posterior translation of the tibia. Injuries to these structures can cause significant disability and compromise activities of daily living and work, recreational, and sporting activities. A thorough understanding of the complex anatomy and biomechanics of the PLC will aid the clinician in this challenging diagnostic and therapeutic problem. The first section of this paper describes the anatomy of the PLC of the knee focusing on the intricate insertion sites of the individual structures. The second section discusses how the anatomy influences the biomechanics of the PLC.

Extensor hallucis capsularis: frequency and identification on MRI

BACKGROUND

The extensor hallucis capsularis (EHC) is the most common name given to the accessory tendon sporadically seen medial to the extensor hallucis longus (EHL). We performed cadaver dissections and MRI evaluation to determine the frequency of its occurrence, the pattern of its origin and insertion, and its potential suitability as tendon graft.

METHODS

The EHC was examined by dissection in 81 cadaver feet. Physical parameters pertaining to EHC size and location were recorded. MRI was performed on six cadaver legs to determine if the EHC can be identified radiographically. MRI images were evaluated independently by a foot and ankle specialist and a radiologist.

RESULTS

The EHC was present in 71 (88%) of the specimens. It originated from the EHL tendon or muscle in 93% and inserted into the first metatarsophalangeal joint capsule in 99% of cases. All EHC tendons were less than or equal to 4 mm in width; only 16% were more than 2 mm wide. Correct prediction of the presence or absence of EHC by MRI varied according to EHC width: two of two in tendons more than 2 mm, five of eight in tendons 1 to 2 mm, and zero of two in tendons 1 mm or less.

CONCLUSION

Up to 14% of the population may have an EHC tendon suitable for grafting in reconstructive surgeries, particularly surgeries related to hallux dysfunction. MRI may have a role in the preoperative identification of the EHC.

Surgical anatomy of the medial collateral ligament and the posteromedial capsule of the knee

The supporting structures on the medial side of the knee consist of a superficial fascial layer (I), a deep capsular layer (III) with the deep medial collateral ligament in it and in between the superficial collateral ligament (layer II). The attachment sites of the different ligaments and the functions of the various ligamentous structures are described and suggestions for surgical repair are given.

Anatomy of the proximal tibiofibular joint

This paper describes the anatomy and function of the proximal tibiofibular joint (PTFJ). The physical dimensions of the joint and the topology of the articular surfaces are described. It is noted that the inclination of the joint is variable, and that joints with a steeper slope away from the transverse plane are less mobile. The ligamentous and tendinous attachments are described. Finally, the histological features of the articular surfaces are presented. The clinical importance of the anatomical features is discussed.

Discal attachments of the human temporomandibular joint

BACKGROUND

Despite its clinical significance, the anatomy of the human temporomandibular joint (TMJ) and its relationship to the lateral pterygoid muscle remains poorly described and often misrepresented in standard texts. The aim of this study was to describe how the anterior and posterior attachments of the TMJ disc vary between lateral, central and medial regions of the joint.

METHODS

Ten left TMJs were removed en bloc from cadavers and serial sections were made at 3-4mm intervals. Observations were made to ascertain the anterior and posterior attachments of the disc and the joint structures were traced from standardized photographs.

RESULTS

Laterally, the capsule and lateral discal ligament merged prior to their attachment at the condylar pole. Medially, muscle fibres, capsule and the disc converged on the medial pole of the condyle. There was no evidence that fibres of the upper head of the lateral pterygoid muscle inserted directly into the disc. The upper head inserted into the condyle either directly at the pterygoid fovea or via a central tendon or indirectly via the capsule. Posteriorly, the superior part of the posterior attachment of the disc attached to the cartilaginous meatus and tympanic part of the temporal bone. The inferior part of the posterior attachment of the disc attached to the posterior surface of the condyle. In four joints, this attachment was folded beneath the posterior band of the disc, creating a wedge-shaped flap that ran medio-laterally.

CONCLUSION

This study is in broad agreement with other anatomical TMJ studies but there are two main points of difference. Firstly, a true muscle insertion of the superior head of the lateral pterygoid muscle to the disc was not observed. Secondly, a wedge-shaped flap of retrodiscal tissue was identified between the condyle and the disc.

Posterior Cruciate Ligament Recess and Normal Posterior Capsular Insertional Anatomy: MR Imaging of Cadaveric Knees

PURPOSE

To analyze the normal pattern of fluid accumulation adjacent to the posterior cruciate ligament and anatomic variations of joint capsule insertion sites in the posterosuperior corner of the human knee by using magnetic resonance (MR) imaging in cadaveric specimens.

MATERIALS AND METHODS

Fourteen fresh cadaveric knees (obtained and used according to institutional guidelines, with informed consent from relatives of the deceased) from 11 men and three women (six left knees, eight right knees; age range, 70-82 years at time of death; mean age, 76 years +/- 4.4 [standard deviation]) were studied with high-spatial-resolution MR imaging performed before and after intraarticular injection of 35-45 mL gadopentetate dimeglumine. MR images were evaluated by two readers in consensus, with emphasis on location of fluid posterior to the posterior cruciate ligament, communication of that fluid with the medial or lateral compartment of the knee, and the relation of fluid to surrounding structures. Readers also were asked to measure, in the sagittal plane, the distance between the posterior capsular insertion sites and the femoral physeal scar. For anatomic analysis, cadaveric specimens were sectioned in 3-mm-thick slices in the sagittal plane that approximated the sections acquired at MR imaging.

RESULTS

In all 14 cadaveric specimens, MR arthrographic images showed a fluid collection behind the posterior cruciate ligament (in the posterior cruciate ligament recess), a finding not evident on images obtained prior to contrast material injection. The recess was distended during flexion, and it communicated only with the medial femorotibial compartment in all cases. Posterior to the posterior cruciate ligament recess, a fat pad was observed in all specimens. Incomplete joint capsule was seen behind the fat pad in seven specimens. Joint capsule insertion was at the level of the femoral physeal scar or between it and a point 15 mm above it.

CONCLUSION

The posterior cruciate ligament recess has specific characteristics that allow its identification: communication with the medial compartment of the knee and absence of the adjacent joint capsule.

Reconciling arthroscopic and anatomic morphology of the humeral insertion of the inferior glenohumeral ligament

PURPOSE

To clarify the morphology of the humeral insertion of the inferior glenohumeral ligament (IGHL).

TYPE OF STUDY

Cadaveric and arthroscopic anatomic analysis.

METHODS

The morphology of the humeral insertion was studied in 200 nonembalmed cadavers through open dissection (100 specimens), by arthroscopy (50 specimens), or both (50 specimens). In addition, the morphology was studied in 100 living subjects with stable shoulders undergoing shoulder arthroscopy.

RESULTS

On the humeral side, the insertion of the inferior capsular fibers is usually in the form of a V, the point of which is covered by the tendon of the latissimus dorsi. When viewed intra-articularly, the inferior insertion usually gives a collar-like impression because the capsular recess is filled with frenula capsulae.

CONCLUSIONS

Our description corresponds with that found in the classic literature. Our results are, however, in contrast with those of others who have observed about 50% of V-shaped insertions. This difference may be explained by the method of observation and by the small numbers of specimens studied. The form of the humeral insertion of the IGHL is linked to the formation of a supporting hammock that can accommodate the humeral head during movement as described by several authors.

CLINICAL RELEVANCE

We believe that the difference between arthroscopic and anatomic observation of the humeral insertion may have 2 major clinical implications. An observed tear of the frenula capsulae may not necessarily represent a humeral avulsion of the glenohumeral ligaments (HAGL). In the case of a HAGL, the capsule may have to be reattached in its V-form to adequately retension the inferior capsule.

The proximal extent of the ankle capsule and safety for the insertion of percutaneous fine wires

We have assessed the proximal capsular extension of the ankle joint in 18 patients who had a contrast-enhanced MRI ankle arthrogram in order to delineate the capsular attachments. We noted consistent proximal capsular extensions anterior to the distal tibia and in the tibiofibular recess. The mean capsular extension anterior to the distal tibia was 9.6 mm (4.9 to 27.0) proximal to the anteroinferior tibial margin and 3.8 mm (-2.1 to 9.3) proximal to the dome of the tibial plafond. In the tibiofibular recess, the mean capsular extension was 19.2 mm (12.7 to 38.0) proximal to the anteroinferior tibial margin and 13.4 mm (5.8 to 20.5) proximal to the dome of the tibial plafond. These areas of proximal capsular extensions run the risk of being traversed during the insertion of finewires for the treatment of fractures of the distal tibia. Surgeons using these techniques should be aware of this anatomy in order to minimise the risk of septic arthritis.

Structural and mechanical properties of the glenohumeral joint posterior capsule

The purpose of this study was to quantify regional variations in material properties of the glenohumeral joint posterior capsule and to compare these data with the anterior band of the inferior glenohumeral ligament (AB-IGHL). Mechanical properties were determined for individual bands of the AB-IGHL, superior posterior capsule (SUP-PC), middle posterior capsule (MID-PC), and inferior posterior capsule (INF-PC). Significant differences in tissue thickness were found among the 3 posterior capsular regions and the AB-IGHL. The AB-IGHL was thicker than the MID-PC (P=.03) and INF-PC (P=.01), and the SUP-PC was thicker than the INF-PC (P=.02). Except for significant differences in failure strains, material properties were not significantly different among the 4 tissue regions. There were no significant differences between tissue bands in modulus (P=.2), maximum stress (P=.46), or strain energy density (P=.62). Specimens failed primarily near the glenoid insertion (75%), with 4 specimens failing at the humeral insertion and 2 others failing in the tissue's mid substance.

The spinoglenoid ligament. Anatomy, morphology, and histological findings

BACKGROUND

Dysfunction of the distal branch of the suprascapular nerve has been reported in athletes involved in throwing or overhead sports. The consistent presence of a dynamic anatomic structure, the spinoglenoid ligament, overlying the nerve in the spinoglenoid notch may be a contributing factor to the dysfunction of this nerve. The purpose of this study was to report the anatomy, morphology, and histological characteristics of the spinoglenoid ligament.

METHODS

The spinoglenoid ligaments of fifty-eight fresh-frozen cadaver shoulders were dissected to evaluate their anatomic dimensions, histological characteristics, and relationship to the suprascapular nerve, the posterior part of the capsule, and the glenoid rim. The spinoglenoid ligament was harvested, with its insertions on the scapular spine and on the capsule and glenoid left intact, for the histological analysis.

RESULTS

Dissection revealed that a spinoglenoid ligament was present in all specimens. The ligament was found to form an irregular quadrangular shape. On gross examination, the deep fibers of the ligament extended from the lateral aspect of the scapular spine to the posterior part of the glenoid and the superficial fibers blended with the posterior aspect of the shoulder capsule. Histological sections demonstrated Sharpey fibers inserting into bone at the scapular spine and blending with the posterior aspect of the shoulder capsule to insert into the posterior surface of the glenoid, findings that confirmed the ligamentous nature of this structure.

CONCLUSIONS

This study revealed the presence of the spinoglenoid ligament in all of the shoulders that were examined, with some variation in the size of the ligament.

An anatomic study of the humeral insertion of the inferior glenohumeral capsule

To define inferior humeral capsular anatomy better, 12 cadaveric shoulders were dissected and an inferior capsular shift was performed. Two types of inferior humeral attachments were identified. In 7 specimens, the anterior capsular insertion bifurcated at the 8-o'clock position (on a right specimen) into a superior internal fold adjacent to the articular cartilage and an inferior external fold on the humeral surgical neck. In 5 specimens, the capsular insertion did not split but inserted over a broad area on the surgical neck. In all specimens, there was a re-confluence of the two folds at the 4-o'clock position. The inferior humeral capsular attachment may extend as far as 2 cm inferior to the articular surface and can be divided into two distinct types, split and broad, each with distinct internal and external folds of the capsule. Failure to release both of these folds limits the ability to shift the capsule superiorly by tethering the capsule inferiorly.

Significance of the latissimus dorsi for shoulder instability. II. Its influence on dislocation behavior in a sequential cutting protocol of the glenohumeral capsule

In a cadaveric instability model that leaves all muscles intact initially, the latissimus dorsi seemed to play a role when complete section of the glenohumeral capsuloligamentous structures did not result in a locked anteroinferior dislocation. The present study was carried out to determine whether the latissimus dorsi does truly affect dislocation in a modified cutting protocol, and to find an anatomic explanation for this apparent behavior. This article (Part II) details the results of a sequential cutting study and relates these results with the anatomic findings of Part I. In 75 shoulders, the influence of the latissimus dorsi on dislocation behavior in the apprehension position after section of all capsuloligamentous structures was examined. After cutting all capsuloligamentous structures, either on the glenoid or on the humeral side, the tendon of either the latissimus dorsi or the subscapularis was cut. Capsular lesions on the glenoid side (20 shoulders) resulted in a locked dislocation in 16 specimens. In the other four shoulders, there was a metastable dislocation after cutting the entire capsule, which did not change after cutting either tendon. With lesions on the humeral side (55 shoulders), three possibilities arose: metastable (17 shoulders), locked anterior (9 shoulders) or locked anteroinferior (29 shoulders) dislocation. This difference in dislocation behavior was related to the variability of the tendon-cartilage distance (TCD) and the type of scapular connection of the latissimus dorsi. A locked anteroinferior dislocation was always observed when the TCD was more than 20 mm, regardless of the type of scapular connection. With a TCD < 20 mm, a metastable dislocation was the result when there was a type 1 scapular connection and a locked anterior dislocation was seen when there was a type 2 scapular connection. The tendon of the latissimus dorsi can restrain the humeral head from dropping inferiorly or can lead to a spontaneous reduction of a dislocation, depending on its anatomy. This effect can only take place in the infrequent situation of humeral avulsion of the glenohumeral ligaments. This may be an explanation for the relative paucity of these lesions in clinical instability series.

Determining the relationship of the axillary nerve to the shoulder joint capsule from an arthroscopic perspective

BACKGROUND

The axillary nerve is out of the field of view during shoulder arthroscopy, but certain procedures require manipulation of capsular tissue that can threaten the function or integrity of the nerve. We studied fresh cadavers to identify the course of the axillary nerve in relation to the glenoid rim from an intra-articular perspective and to determine how close the nerve travels in relation to the glenoid rim and the inferior glenohumeral ligament.

METHODS

We dissected nine whole-body fresh-tissue shoulder joints and exposed the axillary nerve through a window in the inferior glenohumeral ligament. Then we cut coronal sections through the glenoid fossa of ten unembalmed, frozen shoulder specimens after the axillary nerve had been stained with Evans blue dye. All specimens were studied with the joint secured in the lateral decubitus position used for shoulder arthroscopy.

RESULTS

Microsurgical dissection through the inferior glenohumeral ligament from within the joint capsule revealed the axillary nerve as it traversed the quadrangular space. In each dissection, the teres minor branch was the closest to the glenoid rim. The coronal sectioning of the unembalmed shoulder specimens demonstrated that the closest point between the axillary nerve and the glenoid rim was at the 6 o'clock position on the inferior glenoid rim. At this position, the average distance between the axillary nerve and the glenoid rim was 12.4 mm. The axillary nerve lay, throughout its course, at an average of 2.5 mm from the inferior glenohumeral ligament.

CONCLUSIONS

We used two novel approaches to map the axillary nerve from an intra-articular perspective. Our analysis of the position of the nerve with use of these methods provides the shoulder arthroscopist with essential information regarding the location, route, and morphology of the nerve as it passes inferior to the glenoid rim and shoulder capsule.

Non-contrast MR imaging of the glenohumeral joint. Part I. Normal anatomy

MR imaging of the shoulder without contrast is frequently used for evaluation of glenohumeral instability in spite of the popularity of MR arthrography. With proper imaging technique, familiarity with normal anatomy and variants as well as knowledge of the expected pathologic findings high diagnostic accuracy may be achieved.

Recesses along the posterior margin of the infrapatellar (Hoffa?s) fat pad: prevalence and morphology on routine MR imaging of the knee

The objective is to evaluate the prevalence and morphology of recesses along the posterior margin of the infrapatellar fat pad on routine MR imaging of the knee. MR images of 213 knees in 204 consecutive individuals were evaluated with regard to the prevalence and morphology of recesses (a "suprahoffatic" recess close to the inferior border of the patella and the previously described "infrahoffatic" recess anterior to the inferior portion of the infrapatellar plica). The recesses were analyzed with regard to synovial effusion and the condition of the anterior cruciate ligament (ACL). Anatomic dissection was made in 29 knees in 16 cadavers to verify the presence of the suprahoffatic recess. The infrahoffatic recess was present in 45% of the knees and mostly linear in shape (44%). The suprahoffatic recess was detected in 71% of the knees (45% in cadavers). Very weak to moderate positive correlation was found between the synovial effusion or the condition of the ACL and the presence and dimensions of the recesses. An awareness of the recesses in the infrapatellar fat pad is important in order to distinguish between pathology and anatomic variants on routine MR imaging of the knee.