patella

Identity and laterality

Record the evidence identifying this structure as the patella of a particular subject or specimen and side.

1. Which anatomical relationships establish that this structure is a patella rather than another sesamoid, a tibial projection or a loose body? definition
2. What specimen labels, imaging markers or examination records establish its subject, species and laterality? provenance

Ossification and separation

Record the observed developmental configuration and the evidence used to interpret separate components.

1. Which ossified and non-ossified components are visible, and how were their locations and boundaries established? measurement
2. What evidence distinguishes a developmental component from a fracture fragment or unrelated ossified body? boundary
3. Which earlier observations establish whether this configuration preceded the current concern? provenance

Dimensions and bone disruption

Record reproducible dimensions and localised evidence of fracture, loss of bone or remodelling.

1. What are the patella's measured height, width and thickness, and which landmarks and tissue boundaries define each measurement? measurement
2. Where is bone continuity disrupted or altered, and what fragment displacement, separation or articular step is measurable? measurement
3. Which observations support the recorded structural interpretation, and what remains unresolved by the examination method? provenance

Surface and subchondral findings

Record the location, extent and assessment basis of changes on the patellar side of the articulation.

1. Which patellar articular regions are affected, and what extent, depth or underlying bone change is directly observed? measurement
2. Which imaging, operative or specimen observations support the finding and any assigned grade? provenance
3. Which abnormalities belong to the opposing femoral surface and should be linked rather than attributed to the patella? boundary

Height, tilt and translation

Record positional measurements together with the method and pose needed to interpret them.

1. Which named methods and reference landmarks were used to measure patellar height, tilt and translation? definition
2. What values were obtained, at what knee flexion, limb rotation, loading and muscle activation? measurement

Motion path and instability events

Record observed tracking separately from reported or documented instability episodes.

1. How does the patella move relative to the femoral trochlea through the observed range of knee motion? measurement
2. For each suspected subluxation or dislocation, what establishes the direction, circumstances, timing and subsequent position? provenance
3. Does the evidence establish an observed instability event, a reported history or an interpretation of static alignment? boundary

Attachment continuity and extension

Record superior and inferior attachment relationships alongside relevant functional observations.

1. What evidence establishes continuity or disruption at the quadriceps-tendon and patellar-tendon attachments to this patella? provenance
2. What active-extension performance or extension lag was documented, and under which examination conditions? measurement
3. Which limitations can be attributed to patellar findings, and which require linked muscle, tendon, neurological or whole-knee assessment? boundary

Restraint attachments and mobility

Record attachment findings and examined mobility without treating adjacent tissue pathology as intrinsic patellar disease.

1. Which stabilising tissue attachments show disruption, reconstruction or other documented alteration at the patella? provenance
2. What patellar mobility or restraint was observed, in which direction and knee position, using which examination method? measurement

Procedure and residual patella

Record patella-directed procedures, residual native tissue and linked hardware or components.

1. What fixation, resection, resurfacing or attachment procedure was performed, when and according to which operative record? provenance
2. Which native patellar regions remain, and how are implanted components or fixation devices related to them? boundary
3. What residual dimensions, healing changes or device-interface findings are measurable on follow-up? measurement

Management basis and change

Record the basis, authority and reassessment conditions for patella-specific management.

1. Which documented patellar findings support the current restrictions, monitoring or proposed intervention, and who authorised the decision? action
2. What change in patellar integrity, position, articular condition or extensor participation is the next assessment intended to evaluate? action
3. Are follow-up observations comparable in method, knee position and loading, and what uncertainty limits interpretation of change? measurement

Kinds and varieties

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• human adult patella (typically a single sesamoid with a triangular anterior face and a posterior articular surface divided by a vertical ridge into medial and lateral facets, plus a smaller odd facet on the extreme medial margin)
• bipartite or multipartite patella (failed or incomplete fusion of secondary ossification centres, most often a superolateral accessory fragment, distinguished from fracture by smooth sclerotic margins)
• patella alta / patella baja (positional variants: a high-riding or low-riding patella relative to the trochlea, commonly indexed by Insall-Salvati or Caton-Deschamps ratios)
• emarginate or hypoplastic patella (developmental under-formation, including the small high-riding patella of nail-patella syndrome)
• absent patella (congenital aplasia, isolated or syndromic)
• veterinary / comparative patellae (quadruped sesamoids with species-specific facet geometry; horses additionally have a medial patellar fibrocartilage used in the stay apparatus)
• genus Patella (true limpets of the family Patellidae - a different biological kind that shares only the Latin name)

1. Which of these kinds and varieties hold for the sense of patella this model covers, and on what evidence? provenance

Identifiers and schemes

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• Wikidata - Q185021 (anatomical patella); Q131595 (genus Patella) - Two distinct items; do not conflate the bone with the limpet genus.
• FMA - FMA:13386 - Foundational Model of Anatomy identifier for the human patella.
• UBERON - UBERON:0002446 - Uberon class 'patella'; comparative anatomy across vertebrates.
• TA98 / TA2 - A02.5.05.001 (TA); TA2 2588 - Terminologia Anatomica official Latin term Patella.
• SNOMED CT - 64234005 |Patella| - Clinical finding/body-structure concept; child concepts for fracture, dislocation, bipartite patella, etc.
• ICD-11 - NC93.* (injury of patella) and related knee codes; Q74.1 historically in ICD-10 for congenital malformation of the patella in nail-patella and allied syndromes - Use the current linearization; codes shift between revisions.
• ITIS / WoRMS (limpet sense only) - Genus Patella Linnaeus, 1758; WoRMS AphiaID 138322 (verify live) - Applies only if the registry entry is the gastropod, not the bone.

1. Which of these identifiers and schemes hold for the sense of patella this model covers, and on what evidence? provenance

Standards and regulation

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• Terminologia Anatomica (TA98/TA2) - Federative International Programme for Anatomical Terminology (FIPAT/IFAA): official name Patella.
• ICD-11 - World Health Organization: morbidity/mortality coding of patellar injury and selected disorders.
• SNOMED CT - SNOMED International: clinical body-structure and disorder concepts.
• AO/OTA Fracture and Dislocation Classification - AO Foundation / Orthopaedic Trauma Association: patella fracture types (34-A/B/C and revisions).
• Medical Device Regulation (EU) 2017/745 and FDA 21 CFR device classification - govern patellar implants, buttons, and resurfacing components as knee-arthroplasty devices, not the native bone.
• CITES / fisheries and habitat law - apply to some Patella spp. (e.g. Patella ferruginea, strictly protected in the Mediterranean), not to the bone.

1. Which of these standards and regulation hold for the sense of patella this model covers, and on what evidence? provenance

Real-world use

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• Primary landmark in clinical knee examination (patellar tracking, apprehension, grind/Clarke, Q-angle) and in surgical approaches to the knee (medial parapatellar arthrotomy, patellar eversion or non-eversion TKA).
• Sesamoid that transmits quadriceps force to the tibial tuberosity via the patellar tendon; measured on lateral and Merchant/skyline radiographs and on MRI for cartilage and retinacula.
• Common fracture site after direct blow or eccentric quadriceps contraction; treated with tension-band, plate, partial or total patellectomy, or non-operative extension-brace protocols.
• Resurfaced or left native in total knee arthroplasty; patellar component position and thickness are planned to restore offset and avoid overstuffing.
• In horses, the medial patellar ligament and fibrocartilage lock the stifle in the passive stay apparatus; upward fixation of the patella is a recognised veterinary condition.
• If the homonymous mollusc is in scope: intertidal grazing limpets (Patella vulgata and allies) used in ecology, fisheries, and as a Mediterranean conservation flagship (P. ferruginea).

1. Which of these real-world use hold for the sense of patella this model covers, and on what evidence? provenance

Typical measurements

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• maximum height (proximal-distal) - about 40-55 mm in adult humans (sex- and population-dependent; males larger on average) - mm
• maximum width (medial-lateral) - about 40-50 mm in adult humans - mm
• maximum thickness (anterior-posterior) - about 19-25 mm at the median ridge in adult humans; surgical 'rule of thumb' is to leave ≥12-15 mm residual bone after resurfacing - mm
• Insall-Salvati ratio (patellar tendon length / patellar articular length) - about 0.8-1.2; >1.2 often called patella alta, <0.8 patella baja - dimensionless
• Caton-Deschamps index - about 0.6-1.3 depending on source cut-offs; used when the tibial tuberosity is distorted - dimensionless
• sulcus / congruence and lateral patellofemoral angles (Merchant view) - sulcus angle typically ~138° ± a few degrees; lateral patellofemoral angle opens laterally in the stable knee - degree
• Q-angle - roughly 10-15° in men and 15-20° in women in standing clinical measure; method-sensitive - degree

1. Which of these typical measurements hold for the sense of patella this model covers, and on what evidence? provenance

Failure modes and hazards

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• Transverse, stellate, or comminuted fracture with disruption of the extensor mechanism and risk of nonunion or painful hardware after tension-band fixation.
• Patellar dislocation or chronic instability, usually lateral, with medial patellofemoral ligament (MPFL) injury and osteochondral fracture of the medial facet or lateral femoral condyle.
• Patellofemoral osteoarthritis and chondromalacia; overstuffing or malrotation of a TKA femoral or patellar component causing pain, clunk, or accelerated wear.
• Patellar tendon rupture or quadriceps tendon rupture at the poles; avascular necrosis or fragmentation after excessive lateral release or fat-pad excision.
• Bipartite patella misread as acute fracture, leading to unnecessary fixation.
• Patella baja after TKA or tibial tubercle transfer, with restricted flexion; patella alta with reduced constraint and recurrent instability.
• In horses: intermittent upward fixation of the patella (locking of the medial patellar ligament).
• If the limpet sense is used: overharvest and habitat loss of protected Patella species.

1. Which of these failure modes and hazards hold for the sense of patella this model covers, and on what evidence? provenance

Regional variation

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• English common name is kneecap / kneepan; many European languages keep a form of Latin patella (French rotule is the usual clinical common name).
• Radiographic height indices and 'normal' cut-offs differ by school (Insall-Salvati vs Blackburne-Peel vs Caton-Deschamps vs patellotrochlear index).
• Surgical default in TKA (always resurface vs selective resurfacing of the patella) varies by country and training tradition, notably North America vs parts of Europe and East Asia.
• Veterinary emphasis (equine stay apparatus, canine medial patellar luxation grades) is a separate practice community from human orthopaedics.
• Genus Patella is a North-East Atlantic / Mediterranean intertidal taxon; other 'limpets' belong to different families and should not inherit this name.

1. Which of these regional variation hold for the sense of patella this model covers, and on what evidence? provenance

Neighbouring kinds and how to tell them apart

Reported by the breadth pass; each item needs checking against its source before it becomes normative.

• femoral trochlea (patellar groove of the distal femur) - The trochlea is a femoral articular surface; the patella is the mobile sesamoid that rides in it. On a true lateral radiograph the patella is the anterior ossific density separate from the femoral condyles.
• patellar tendon (ligamentum patellae) and quadriceps tendon - Soft-tissue continuations of the extensor mechanism proximal and distal to the bone; MRI or ultrasound shows fibre signal without cortical bone, except at entheses.
• fabella - A sesamoid in the lateral gastrocnemius tendon behind the knee, not in the quadriceps tendon in front of it.
• tibial tuberosity / Osgood-Schlatter fragment - Apophysis of the tibia at the distal patellar-tendon insertion, well distal to the patella on a lateral radiograph.
• bipartite patella vs acute patellar fracture - Bipartite fragments (usually superolateral) have rounded, corticated, matching margins and often contralateral symmetry; acute fractures have sharp non-sclerotic edges, marrow oedema, and a compatible injury history.
• prepatellar bursa (and housemaid's knee swelling) - A subcutaneous synovial sac anterior to the patella; fluctuation and absence of bony disruption on radiograph separate bursitis from osseous pathology.
• genus Patella (true limpet) vs anatomical patella - A marine gastropod with a conical shell; identified by taxonomy (Patellidae), habitat, and radula, not by knee anatomy. Shared Latin name only.

1. Which of these neighbouring kinds and how to tell them apart hold for the sense of patella this model covers, and on what evidence? provenance